I agree with everyone about Gotti biding his time and all, but to answer the latter part of the question, there are more than a few informants who now live in plain sight. The modern day thinking is that there's no upside to killing a rat after he's already testified. If they could get to him before he testifies, that's one thing. But once the damage is done, the feeling today seems to be that killing an informant just brings too much attention from law enforcement.