It finished successfully at some point overnight. I honestly didn't look at the completion time.
My temporary fix before this was to pull back the 388GB of demo material off of the FlexRAID array. I had put about 250GB back before I rebuilt the parity drive, so this morning I started copying the remaining 138GB to it and set up a scheduled update that should have kicked off about 25 minutes ago. So far, knock on wood, no error email. I should have set it to send me a "success" email as well, but since I can't do anything with it until after work anyway, I will just assume that "no news is good news" especially since Updates would error out within about 20-30 seconds of starting before.
I am sure that there was a "less destructive" fix, but it was getting late, I was frustrated about this and about spending 2 hours on the phone with an work issue because someone else screwed something up, so I went the "start over" method figuring that as long as a data drive didn't fail, that I would get the cleanest parity drive fix.