I could see them more likely offering TSMC a partnership in a new fab, especially given that TSMC are looking to expand further out of Taiwan. That would be more cost effective than starting again from scratch.
TSMC have little incentive to do so, as AMD are not their biggest customer.
AMD are supply contstrained - when they make good CPU's (Zen3 launch for example) they can't make enough stock to satisfy demand. They are also at TSMC's mercy, and have to swallow any price increase TSMC throw at them. Also, Apple get first dibs for the newest nodes etc.
I'd far prefer AMD to have it's own fabs that are competitive with Intel's, it would make AMD a much bigger threat.