Simple answer is - nobody knows.
If it's a Hard "cut all ties" Brexit it might end up as you describe, but we might also end up with a Soft Brexit where nothing much changes, and any number of mix'n'match options in between.
It will all be part of the negotiations after Article 50 is invoked. The issue hasn't been ignored (plenty of discussion on these forums), but everybody is guessing cos its never happened before. Air transport arrangements won't be at the top of the Governments "to do" list (it'll be behind things like immigration and trade...).
There's an awful lot to be done in two years.