Use legaleese to fight legaleese, just write in the ToS itself only the blockchain version is applicable. If they want to move off they at least have to update the blockchain version to remove the blockchain requirement for applicability.
They could of course just do that, so there is no benefit from it being in block chain compared with anywhere else.
The only advantage block chain provides is you don't have to trust anyone.
Eg you don't have to trust GitHub to not delete or modify the repo themselves, but they weren't any part of the problem here.
Blockchain history cannot be manipulated unlike in git. This was meant as a joke though. There’s other ways to achieve this besides blockchain. the internet archive way back machine can pull up the TOS on a certain date.