The problem is, how do you reassign the funds after the hardfork? The funds are attached to addresses and not persons.

You can revert the funds to the address that paid into the contract in the first place, since transactions are public.

That wouldn't move the money to their rightful owner but to the previous owner.

I don't think that's correct. If you only revert the stolen money transactions and all the branches of them since, almost nobody loses. The few stolen ETH that got sold will be a loss, but it's nothing compared to $35M.

And you'll revert them to what? the buggy contract?

It's a hard fork. The contract would be fixed. But you could also send the victim's money anywhere, just ask the victim where they want it, there are only 3 major ones.

Start at block n-1, disable the buggy contract, leave the "stolen" funds where they were.

They were in the contract (or the contract addresses).