Well, I forgot to put the temp probe back in the chest freezer after cleaning it out and placing new kegs in. So, 12 hours later, I have found frozen yeast slurries in 1 qt Ball jars. Are they goners? I have taken them out to allow for them to return to basement temperatures (55-60 F) before returning them the chest freezer (if they are OK). My gut says that I have reduced some of the viability. I imagine the beer will be fine once it acclimates.
Some if not all of the yeast will be dead. You could try making starters and see if it works. But I wouldn’t bet on it.
I bet you could make starters with it but you definitely killed a large portion of them.