I have no confidence in governmental agents, but civil action will be likely to have nominal grounds to proceed IMHO (IANAL), and the blatant theft of these funds will strongly favor the plainfiffs that have provably been harmed by the takeover of the blockchain this theft caused, even if the funds are eventually returned.
These exchanges took the money and acted as if it was theirs, and are STILL depriving the rightful owners of that money full possession and use of it. That's theft. They should go to jail AND they should pay damages.