Sorry for dragging this offtopic.
Parity check isn't going to affect filesystem one way or the other, since even a correcting parity check will only write parity, and has no effect on the filesystem of any data disk. If the power failure causes a filesystem corruption, that would have to be dealt with on its own. So whether you complete a parity check now or later is a separate issue.
Best to have an UPS as mentioned and avoid these potential issues.