When to adapt is a valid question because as you mentioned moving too late would mean Bitcoin holders are in trouble and moving early or without consensus will have its own problems. Eventually all forms of technology will adapt and an example is quantum computing. If Bitcoin adapts to become quantum resistant then no doubt other form of computing will emerge and then Bitcoin will adapt, the cycle will continue.
Maybe a couple of decades from now, in the end it might be a case of Bitcoin not having a way to protect itself and it simply becomes overpowered by the threats that emerge - who knows.
Bitcoin and altcoins need to adapt to any perceived threat before they can cause any harm therefore need to be prepared for any and every eventuality.
Yes, definitely. The question is
when should bitcoin adapt, and that is a balancing act.
Move too late, and people won't have sufficient time to move their coins to quantum-safe addresses.
Move too early, and there will be chaos as a) there isn't a consensus on exactly what is the best quantum-safe cryptography to move to, and b) as QCs are still widely considered a future rather than current threat, the inevitable disagreements about whether or not to burn coins that don't move could erupt into civil war, or if not that then people would at least separate into opposing camps and begin to become entrenched in their opinions.
It's a difficult situation, but I am an amateur with only a superficial understanding of the various possibilities, and fortunately the people who have to make the decisions here are far smarter and more knowledgeable than I am. I may have little faith in politicians, but I have considerably more faith in bitcoin devs.