Well, it wasn't discussed how they managed to retrieve the elixir without conquering the elves, but I decided to not press the matter further.
At the very least, it seems there wont be any further attempts to attack the elves again. Due to the substantial losses incurred during the war, the idea of going back to subdue the elves had become quite unpopular; with a certain group of nobles returning from the war, leading the opposition.
It seems I wont need to return to defend the elves for the time being