What if I don't join someone for postdoc to whom I previously applied
If your situation has genuinely changed—six months or a year go by and you’re working as a postdoctoral or researcher somewhere else, why would you be expected to give up your position? This seems like a very one-sided transaction and unfair to you. Might the professor hold a grudge? It’s possible, but anybody who does hold a grudge in such a scenario is thinking primarily about their own needs rather than your mutual benefit.