Hi Quidnunc,
Are all the roots dead or are some OK? Dead roots are hollow or mushy, good roots are firm.
If some are ok then cut away all the dead ones and pot back up in the very smallest pot that you can fit the remaining roots into. You might want to use an old food container with holes punched in it if you can't find a small enough pot. If the plant is then unstable as a result use an empty larger cache/cover pot to hold it.
Water when the medium dries out, the reason for the small pot is that it should dry quickly, allowing you to water often without rotting the roots.
If all the roots are dead then it is going to be much harder, especially as the leaves are already dehydrated. To be honest I've never been successful when they have got to that stage although others here on OB have. I believe some have had success with
Sphag-n-bag although it didn't help me. Others have had success with water culture which you can probably find info about here on OB, but again it didn't help me.
Good luck, hope you manage to save it.