Yeast is extraordinarily resilient and is all around us, on us, and (as far as I know) in us to a certain extent. The original beer recipes didn't call for a quick jog over to the local general store for a packet of yeast. Enough yeast (in a non-sanitized situation) would just be in the barrels or vats or whatever to guarantee fermentation. The quality was pretty variable but the end result of fermented mash was just about guaranteed.
In fact, you can grow your own sourdough starter today without intentionally putting in any yeast ... in your own kitchen with things you likely have laying around already (assuming you have flour, water, maybe some sugar, and a decent container).
Reason for me bringing all this up? The idea of these frankenyeasties making out into the wild is troubling. If they crowd out wild varieties, the results could be terrifying.