Other things can adapt but how does bitcoin adapt? Or are people willing to just give up all the old coins as if nothing happened?
Just like every other existential threat to bitcoin QC will threaten other more important things, like infrastructure, first.
It's a non-threat.
It seems like the only options is to either just let it happen or make those bitcoins disappear.
And then the community could decide “if you didn’t update your addresses before quantum computer attacks were viable, even though you had 5 years to do it with strong evidence that it would be necessary eventually, and lost your coins as a result, then sucks to be you”