Rollback would fix it, but I highly doubt that they have a save from back then, unless the world auto-saves without us knowing.
Some Op Prison players have decided they want a reset. I find it absolutely horrendous, that they would go and do this.
I used to play OP Prison a lot but now... Not so much as I got really bored and tired but to see this happen? Wow... People really need to keep there act in line and not do this...
Thanks for letting us know, I managed to fix it the best I can. I also added a world guard region with blocked-cmds /plotme claim, /plotme clear, /plotme reset.