If they decided to go fabless (something I'm very much not convinced of, I think it is too early to throw in the towel) they wouldn't just abandon it and let the tumbleweeds take over. They'd sell it, and their other fabs that have new enough technology, with TSMC and Samsung the most likely buyers.
You can't just quit making your own chips and start buying someone else's, as many have pointed out TSMC doesn't have the capacity to absorb Intel's business. But if Intel turns over their fabs, with Intel staff operating them as an Intel fab until TSMC was ready one by one to upgrade them to do TSMC technology and take over operations. Presumably most of the employees would stay on, it would just be the upper management that TSMC would need to replace.
Samsung might be a more likely partner, just because TSMC is already so big and unlike TSMC Samsung has a lot of excess capacity currently. They are having trouble keeping up with TSMC, but they wouldn't if they had big customer like Intel paying the bills to develop new processes. Just make sure they check resumes carefully so they don't accidentally hire any former Intel managers!