First: Make a copy of your campaign. Which is usually a good idea to do occasionally anyway. Second: Switching sheets is almost never a good idea, unless the sheet or a script gives you some sort of migration assistant. All sheets use their own set of attribute names and you will never get a 1:1 data transfer. A sheet should be chosen at game creation. I did the opposite a couple of years ago, switching from Shaped to the D&D 5th Edition by Roll20 Sheet. I rebuilt the campaign. I would think that switching back to the official sheet should restore your sheets to their working state, but there may be unexpected results. In any case, do this on a backup game first and look for problems. If you only really need to rebuild the PCs, and most of the NPCs are stock monsters, then make a backup and replace all the characters manually. PCs will take some time, NPCs should mostly be drag and drop, depending on how you set them up to begin with. Good luck!
