The RN would have to interdict the second invasion with all of the North Sea coast of Europe held against them and the Skaggerak heavily mined. The chances of the RN in late 1940 or early 1941 putting its head in the noose to save Southern Norway is nil in my opinion.
Hitler does just that in terms of squeezing an invasion in between July 1940 and May 1941 - he was preparing for Sea Lion IOTL. In this TL the resources get diverted to Norway. He managed to invade Yugoslavia and Greece almost at the drop of a hat.
Most of the destroyer losses would be replaced by the 36A builds and the RN doesn't have hundreds of destroyers to deploy - thay had 164 at the start of the war across the world. Remember in September 1940 they were so short of escorts for the Atlantic that they had to beg 50 WW1 destroyers off the USA. So they hardly have hundreds spare for Norway.
If you had bothered to read my post before you went into flame mode you would have noticed that I didn't say Germany could take all of Norway second time around - only up to Trondheim / Mo i Rana. And for the British holding on to Narvik is probably good enough for their defense of Norway.
Still none of this makes sense to me, maybe you need to explain it better.
What is the relevance of Germany possessing e.g. Netherlands or Schleswig when Britain can easily reinforce from Scotland to Stavanger, well beyond reasonable German reach? What seems far more relevant is that Denmark is full of German aircraft and a handful of German ships, while Norway would be full of Allied aircraft and more allied ships. How are the Germans going to heavily mine a waterway actively contested by air and naval forces, and in a way that prevents the allies sortieing from Norway to attack the invasion but still allows the German invasion to sortie into Norway? How does German air power from Denmark manage to sweep allied navies from the open sea (despite allied air cover) while allied air power from Norway is magically unable to interfere with German landings on the Norwegian coast, minutes from Norwegian bases but (at least) the same distance from Danish bases as London is from France?
I do agree that in “late 1940 or early 1941” it’s extremely unlikely the RN would do anthing to save Norway, because that is winter and any invasion attempt in that season would be a guaranteed disaster even without their intervention. The available windows for a non-suicidal invasion are late summer 1940, I.e. taking the pressure off the British in favour of menacing the Norwegian fjords, or early 1941, I.e. distracting even more from Barbarossa than OTL and giving the British a ready excuse for dodging a half-arsed intervention in a marching war on the wrong side of the continent in favour of a naval war in their back yard. A second Norway instead of the Balkans is a gift to the brits.
From the British perspective Inverness-stavanger is what, 650km, 18 hours on a fast ship through friendly waters. Plymouth to Piraeus is 5300km, at least six days on a fast ship to the complete other side of a war zone with a hostile Italy in the middle of it. From the German perspective Yugoslavia and Greece are both a couple of train tickets and some marching away, Norway is an amphibious invasion (without a fleet) away.
I take your point about the perennial shortage of British escorts, but the fact is that they had a lot of them (and corvettes, and cruisers, and armed trawlers, and yadda yadda yadda), were building more new ships faster than the Germans, and were getting stronger at sea all the time. Whereas the Germans would be hopefully replacing “most” of their losses (if they don’t lose even more contesting the Skagerrak). For the British, expending a bunch of ships to finally wipe out the kriegsmarine and secure their east flank is a straightforward calculation.
Lastly, if you had bothered reading my post you would have seen that I specifically addressed Mo-I-Rana. I repeat, to me it seems much more likely that if the Germans were to reach that far north the allies will just wash their hands of the whole scenario. German uboats, coastal craft and aircraft based along the Norwegian west coast transform the whole situation and turn the UK supply line from a protected interior route into an exterior, exposed route. The strategic danger of losing the east flank has already come to pass, in 1940/1941 Stalin is a Nazi ally so access to Murmansk is a non-issue, what is to be gained from battling away against superior German forces (and they must be pretty damn superior to have pulled it off on the second attempt)? Why would the allies not just cut their losses? If the iron ore was a concern they could thoroughly demolish the railway from the Swedish border to the sea, and wreck Narvik completely. Much more cost effective than trying to hold on to a tiny port that has no value other than denying it to the Germans.