Because of how I do things / what I play with, I'm probably very harder on the array than most users (with regards to unclean shutdowns), and I have never once had file corruption / unmountable drives, etc using XFS.
If the drive(s) come up and are mountable, then you're not going to experience any major problems. Worst case scenario pretty much is a file or two that *may* be corrupted (if a parity check indicates errors). All of your "If I lose this my wife will kill me" files should be backed up onto physical media / cloud / whatever.
Every computer should have one. Corruptions caused by power loss on not limited to unRaid, but affect every OS equally.