GA survives in a precarious balance. As with any activity, there are those who participate who will afford any price for their pastime. Those people are not the commercial airline pilots of the future. But, to a large degree, GA flyers just manage the costs to fly, in an environment where really no one is making much profit, and everything is more costly and complicated than ideal.
We linger on with mainstream certified flying still following the WW2 model of how to build and maintain planes, and train pilots. The problem is that the GA fliers don't have the military budget for any of that. Non certified aircraft can be less costly to operate, but pound per knot per dollar/pound moving much more than one or two people at more than 90 knots gets pretty costly - before things change for the less good, as they will.
I imagine fuel availability and the stigma associated with huge fuel burn for poor person per mile efficiency will make GA socially unwelcomed. Society won't care that it's highly convenient for a few people to fly direct and save a few hours of driving time, or to bimble around on a pretty evening. The public will brand aviation gasoline as bad because they don't do it, as they have with aircraft noise, and regulate it to death.
Electric will help, but it will be a long time before more than two occupants can go further than the next airport on electric. And the cost will be immense to develop and build those new or modified aircraft.
And now the airlines are trying to circumvent the traditional pilot experience building path - GA flying. If wannabe commercial pilots aren't "hour building" as much, a large market is no longer there to sustain the rest of the fleet, who just fly recreationally.
As WW2 vintage aircraft still fly, so will the Cessnas and Pipers of the '50's through '80's, in the decades to come. But I fear that they'll do it in warbird numbers - not many!