I wouldn't count on anything, though I sincerely hope all these nice optimists are right!
The airlines will still exist in some form. Airlines will almost certainly return to the regulated status of the past, and commercial aviation will be more like it was in the 1950s. Airlines will have a much smaller share of the overall transportation market, and rail passenger travel will expand dramatically to accommodate the core market for transportation.
Air travel will cost much, much more 20 years from now than it has in our time, and only rich people will travel by air on any kind of regular basis. For most of us, an airline trip will be a once-(maybe twice)-in-a-lifetime experience, and we will keep all the souvenirs.
If you want to go visit aunt Alice in Peoria, you will do it by train, which will be a much more comfortable and enjoyable way to travel than air travel has been in the last 40 years or so.
In fact, the transportation scene will tend to morph into a system based on a combination of small electric vehicles for local travel and passenger trains for intercity travel. You will lease an electric buggy for zooming around town. When you need to go to Chicago, you will drive it down to the railroad station and plug it in; then you will get on a train and ride in comfort to your destination city. When you get there, you will stick your card in a slot and check out an electric car identical to the one you use at home. Drive to your appointment, and when you are ready to go home, reverse the process.
As for general aviation, I tend to agree with the optimists. Clever people who want to fly will continue to figure out ways to do it. As the volume of air traffic in general declines, the airspace system can become simpler, and personal flying will become more fun.
In general, look to the way things were in the 1950s. That's what it will look like 20 years from now.
retired airline captain