Sacrosanct
Legend
I would say a wish or something similar would be needed now to return this wizard to a living person again. Perhaps a plea or request to a deity from a VERY faithful cleric in exchange for completing an extremely difficult quest. A great excuse for a new adventure that may or may not be related to what is currently happening in the campaign.
These were my exact thoughts when reading the OP. The 5e cleric even has a class ability specifically for things like this (divine intervention)