Over-proofed pizza dough, pâté fermentee? So I made this pizza dough. I started it with a biga, then put it into the fridge for cold rise. Then I got kinda sick, and the dough stayed in the fridge for, like, four days. I’m afraid it’s over-proofed, and the yeast has crossed that rainbow bridge.

I’m gonna make the pizza anyway, but if it turns out that it is over-proofed, can I still use a small piece of it for pâté fermentee? Or is that just pointless?
Sure, go ahead and use it. That's exactly how preferments are made. As long as it doesn't have obvious spoilage signs (mold, ropiness) it's good to mix in in proportions up to 50% of the final dough.