In a follow-up to his tweet that for proton decay, hope springs eternal, Frank Wilczek (of QCD Nobel Prize fame) tells us, that proton decay has a finite life time even in the Standard Model. That’s interesting, I didn’t know that!
Over at physics stackexchange, however, people are a little bit divided over this issue (or don’t read the question carefully…)
A similar question is discussed here.
It seems to be the case that while proton decay does exist, it is for all purposes unobservable. Nice to know!