How to save classical chess?
Carlsen is doing nothing different than what Fischer and Kasparov did. He is trying to force his rules on FIDE or else he will not defend the title. The difference between Carlsen vs Fischer and Kasparov is Carlsen wants to destroy classical chess and make the world title nothing but a bunch of blitz games mixed in with classical time controls and even the current classical time controls are probably too long for Carlsen. The time controls for the world title used to be 40 moves in 2 and 1/2 hours.
I think Carlsen is getting tired of classical chess just like Fischer did because to him it is "boring and stressful." If he wants to limit himself to blitz tournaments online and leave the classical tournaments that is up to him. But he shouldn't be allowed to destroy classical chess for his own selfish reasons.
Fischer wanted:
1. Not counting the draws, first to win 10 games wins the Championship.
2. If the result is 9-9, then the title goes to Fischer but the prize money is split equally.
3. There will be an unlimited number of games.
Kasparov wanted to replace FIDE and its president Campomanes. "It is war to the death with him as far as I am concerned. I will do everything I can to remove him”. So he formed the Professional Chess Association (PCA),
Carlsen wants to destroy classical chess.

How many times have you heard an analysis of a Stockfish or AlphaZero game and the analyist says 'in this position, a human GM would play [some typical move]' where AlphaZero ignores it and does something else, and 9 moves later the reason becomes clear.
This is because human chess has stagnated. Chess is hard, time to go to the next level and learn from the machines.