There are forks which will keep the sanity alive, but I worry about how long Firefox will survive if everyone moves to them, and I have doubts about how well those forks will be maintained after Firefox is gone.
But seriously, web is asymptotically approaching zero usefulness precisely because of all those "capabilities". In those circumstances, can't you see a million nerds muttering "we'll build our own interweb! with blackjack and hookers!" And one of them might even get lucky, and get a tipping point. Gemini's just an example.
I don't think web's ever going away for corporate stuff, but I can imagine the cultural party moving next door, to a less capable protocol.