In the event that Amin does destroy the causeway it could result in some real foreseeable problems.
1. - The Tanzanian troops would be unable to directly advance towards Entebbe without approaching the outskirts of Kampala first.
The impression I got from at least some of the articles was that the 207th was directed towards Entebbe
through the swamp and not via the causeway (perhaps there was some minor roads or so? Unless they meant the 207th was meant to advance along the causeway up to a point and then veer off towards Entebbe)
2. - Would the Tanzanian troops decide to advance on Kampala without capturing Entebbe which would be defacto Suicide as they would be exposed to possible flanking attacks from the Ugandan and Libyan troops. And failing to capture Entebbe would allow Libya (Or any country that suddenly decides to assist Amin) to send in reinforcements.
The original plan was to approach Kampala from 3 directions and leave the way open for the Libyans to exit via Jinja. Entebbe was already being used to ferry in Libyan reinforcements, so I don't see that changing and by this point Amin is very unlikely to get assistance from anywhere else; certainly not the United States, France or the United Kingdom and the USSR actually stopped sending equipment to Amin during the conflict. Meanwhile China sent none to Amin and sent a token amount of equipment to Nyerere of Tanzania. Libya herself was also
becoming heavily involved in Chad (much to France's disapproval and France's active counter-intervention). Libya had already made enemies
with Egypt by this point. In fact, Idi Amin's
behaviour had also managed to get him on France, the US, Israel
and Kenya's shit list and his regime was generally regarded very poorly after the Air France hijacking and his role in it.
The Libyan forces in Uganda suffered numerous problems including massive linguistics barriers as none spoke Swahili, few spoke English and most persons in Uganda simply don't know Arabic. So for example when the Tanzanians surprised the Ugandans and Libyans at Entebbe in OTL, the Libyans were so disrupted by it and so out of their depths at this point that they didn't know the way to Kampala from Entebbe and could only go around asking residents for directions by just saying "Kampala". Local residents either attacked them or pretended to show them the way by leading them to the Tanzanians (this is also another factor that cannot be overlooked - once the Tanzanians entered Uganda the locals at first quietly supported them - posting messages on trees asking them not to leave Masaka and Mbarara lest Amin massacre them (which he actually promised to do in a broadcast) and then more openly by providing water and supplies to the Tanzanians and Ugandan rebels (and carrying their equipment) in their advances from Masaka and Mbarara and by providing information on the whereabouts of Amin's soldiers and cheering and celebrating whenever they entered a new town).
Additionally in a lot of the articles I posted (as well as articles on the individual battles) what stands out is that the Libyans and PLO never stood their ground once their Ugandan allies retreated (which makes sense, why the heck would they want to defend a position in Uganda if the Ugandan Army itself was fleeing? It's not like they are defending their own country). The Tanzanian forces also apparently never shied away from combating the Libyans and even sought to engage them whenever they could (for various reasons, one was the challenge by Gaddafi, another was the fact that for some in the Tanzanian forces they saw the Libyans as attempting to convert the Ugandans and I suspect that part of the motivation was that they resented the intrusion of Libya into East African affairs).
If the causeway is destroyed then since the Tanzanians anticipated this (by having the 208th directed to advance in a sweep around the swamp) they would probably continue with the contingency and perhaps utilize 205th and 206th in their sweep through northwestern Uganda to come in to Kampala from the north. Additionally with the causeway destroyed the Tanzanians can leave far fewer forces in Lukaya because just as how they can't attack Kampala from the causeway, so the Ugandans and Libyans also couldn't attack into Lukaya/Masaka from Kampala via the same causeway. So instead of just the 201st (which apparently was one of the least experienced/greener of the Tanzanians units) facing the Ugandan Tiger Regiment, they might well send
both the 207th and large parts of the 201st north to account for the Tiger Regiment which means the engagement at Sembabule probably doesn't last nearly as long as 3 weeks.
So original battle plan:
(purple is a move that I think was intended to happen (and might have happened but I haven't seen it mentioned) via the 208th's original movement)
Possible battle plan (one of many variations open to the Tanzanians really) that could have happened if the causeway was destroyed:
Nyerere never wanted to Libyans to be completely encircled as he wanted them to have an escape route (which was a good idea as it meant they had less motivation to fight like a cornered animal if they could flee). So either a move into Kampala from the west, northwest and north would leave the Jinja route open, or the Tanzanians opt to encircle Kampala and the route left open for the Libyans is Entebbe with Nyerere sending a message to Gaddafi as in OTL that Libyan evacuations would be allowed. In the latter case if Gaddafi decides to double down on stupidity (something he was very capable of) and not withdraw his forces via Entebbe then when Kampala is liberated, the Libyans have major problems:
1. In OTL, the imminent collapse of Amin's regime saw the Ugandan Army units in Tororo (that had previously defeated a rebel Ugandan push from Kenya during the war) defect en masse to the rebels. The fall of Kampala will embolden Ugandan Army units to switch sides or completely demoralize them as in OTL such that they won't put up heavy resistance and will likely try to take on cover as "civilians". If defection to the rebels happens in Entebbe, then the Libyans might find themselves stuck with an enemy in their midst.
2. The Tanzanians will now have a large portion of the Ugandan civilians on their side who will likely assist them into Entebbe in moves meant to surprise the Libyans and Amin loyalists (in the moves towards Masaka and around to Mubuendi the Tanzanians had the aid of local persons as guides and people from areas near the border in Tanzania who could speak to locals in Uganda and gain very useful information).
3. - What if the Ugandan and Libyan troops manage to set up ambushes along the only routes to Kampala from the west (Destroying the causeway could easily open up such a opportunity for such an attack).
Given the comedy of errors that the Ugandans and Libyans did in the counterattack towards Masaka and the fact that regional divisions meant that Ugandan troops from northern Uganda did not see this as "their" fight but as a southern affair - some units even thought that because the Suicide Battalion had started the whole war by invading Tanzania, then it was the Suicide Battalion's job to defend places like Masaka - I doubt that they would be able to effectively do this in such a way as to completely stall the Tanzanians on the way to Kampala (much less endanger the whole venture). I think their best bet was dislodging the Tanzanians at Masaka when they had the chance of the counterattack but they let that opportunity slip in a massive way and the Tanzanians regrouped very effectively (reading about the battles what stands out is that the Tanzanians consistently
out-thought their opponents, in the battle of Lira for example the commander there ingeniously decided to approach Lira from an unexpected direction (and managed to get transportation across the lake, again using his head) and to use a portion of his forces as bait
and as a blocking force).
What would likely happen is that for Tanzania to approach Entebbe is to go through Nsangi then southwest to Mpigi in order to do so with the main route to Kampala from the west if successfully secured quickly (Depending on the effectiveness of the Ugandan and Libyan troops). If they successfully capture Entebbe through the routes I mentioned Tanzania will still be able to advance onto Kampala with no threat of any flank attacks or any Libyan reinforcements.
Indeed, as the road network would seem to allow them to branch off and attack Entebbe anyway before advancing on Kampala, like so:
The actual reasons that Tanzanian troops decided to capture Entebbe (After they had advanced to Mpigi) before advancing onto Kampala was to prevent the Ugandan and Libyan troops from being able to launch a flanking attack when the Tanzanians launched their assault on Kampala and to prevent additional Libyan reinforcements from entering the country.
More the former than the latter I would say as Nyerere definitely told Gaddafi that Libyan troops could be airlifted from Jinja. Which suggests that if the Libyans really wanted to they could fly reinforcements
in via Jinja as well (there was also an airbase at Nakangole too I think from what I was reading).
