Quite possibly. But as I see it, the southern mountains are of limited value to Italy and can be used as a bargaining chip to get concessions or support elsewhere. What is important is control of the Otranto Strait with Valona and its bay (Sazan included). Now I am pretty sure that the mistress of the seas, a certain Albion, is reluctant to see other naval powers controlling strategic choke points. Fiume and Trieste will control almost all the austrian trade and a significant part of the czech and hungarian trade. By turning the Adriatic into an italian lake, Rome gets valuable economic influence over the former AH states. It makes certain sense for the rest of the Great Powers not to give a big hinterland for Valona to Italy.
In OTL, even without an italian Valona, the Powers were very close to give south Albania/northern Epirus to Greece. Now they just have much more incentive.
It is not what Venizelos wants... It is what the Great Powers allow Venizelos to claim. Moreover, from what I get, is that it would have been difficult for the Italians to simply seize Valona, as it was part of an already established state- a state established as a compromise between the Powers. It is not the same with Fiume, spolia from the rotting corpse of the AH. If a unilateral action in Valona is unlikely, the fate of Albania will have to be the product of negotiations between Italy and the big ones. As always, it has to be the end result of compromises, as Italy doesn't have enough leverage over the other Naval Powers.
While you are generally right that North Epirus is not strictly necessary for Italy due to the control of Vlore (Italy already have military from 1915 control of the city and basically all southern and central Albania, North Epirus included having displaced Greeks troops inb 1916), Sonnino is hardly the one that quietly give up something freely even useless things and on the other side Italy will ask a demilitarization of North Epirus and Corfù and/or Athens giving up any claim over the dodecanese. The OTL agreement was much due to the situation with Jugoslavia and the need to concentrate there all the diplomatic effort, plus many thoughs that by giving up something in an area, Italy will have been compensated in another...here the scenario is different and Sonnino can go for an hard bargain and i don't know if Venizelos is ready to accept that terms.
In the end Italy will be 'convinced' to give up to Greece the zone? Probably, but i expect Sonnino to drag this question as long as possible.
Italy has faced somewhat less carnage in TTL, so they can pacify their chunk. They will face only irregulars after all. So, short term they can certainly keep their colony. Long-term it is difficult without a change in demographics. A potential policy that helps in maintaining the colony is land reclamation in the malarial coastal regions along with expelling the current peasants towards the interior and forming small italian agricultural communities in fertile enclaves along the coast. Or perhaps, have an agreement with Greece to expel the greek minority (in return for e.g. recognizing greek claims in northern Epirus) and settling the former greek villages (most of them on the coast after all) with Italians. A generation later, Italian Anatolia may develop to an algerian-style decolonization conflict that will result in partition of the region. That is the best plausible senario I can see for Italy to keep a small part of Anatolia until this day.
Honestly the italian zone becoming a full fledged colony it's a 50/50 people were a lot undecided over his fate, a group wanted create a colony but another wanted simply getting a treaty that will have given Italy economic dominance of the zone. In OTL the second group won (even if such victory was phyrric) and helped Ataturk against the Greeks so to keep the treaty that they have just signed with the Ottoman govemrment due to the Turkish seemigly too strong to be put down easilyand a permanent occupation being too costly...naturally Ataturk immediately throw such treaty in the dustbin as it was very loopsided, ITTL can go both way