"Dealing effectively with this virus while we do not even now have a clear understanding of how it is transmitted seems unlikely.
Airlines will have a hard time convincing people that travel is safe as long as that uncertainty remains. That suggests this crisis will be resolved only after a vaccine has been proven efficacious.
It will be a two year event in that case at best."
Good post.
Although I think you can amplify the "two year event" part. Outside aviation the gradual return to "normality"* will happen more quickly than two years. In many parts of the developed world life will look at lot better as early as February/March 2021...irrespective of the delivery of an effective vaccine. Even the worst case modelling shows the second wave peaking by January at the latest. Super fast testing and ever improved track and trace will do what nature does not.
However, the event duration in aviation terms will be far more "long-tailed" (pun intended). The reasons why have been argued over endlessly on here since March, so I'll merely say 200 odd sovereign states agreeing and lining up all the holes so international air travel can take place smoothly again is going to take time. And that is only one of the factors. In aviation terms two years is optimistic, but optimism is probably a good thing right now (for most of us).
*[air quotes, because I don't believe in the concept of "normal" - the world moves too quickly for that word to have any realistic meaning in this context]