I don't think this is going to work. Time is on the side of the attackers. All the attackers have to do is wait and repeatedly restate that they will fully rest

I don't think this is going to work. Time is on the side of the attackers. All the attackers have to do is wait and repeatedly restate that they will fully restore operations if the victim pays a small fee and when losses grow large enough investors / shareholders will apply enough pressure to management to make it happen, whether it is legal or not. No one is going to eat massive losses for the greater good. There are plenty of policies against negotiating with kidnappers and terrorists, and yet people still do it for this exact reason. Banning crypto exchanges is actually a much more effective solution to the problem because it at least forces someone to show up in person to collect the money.