It shows in the final Godfather film that Michael deeply regretted killing Fredo,
Did he really? He told the Cardinal in his "confession": "I had my brother killed--
he injured me."
Well crying like a little bitch and confessing to the future Pope is a sign to me that he regretted it... remember he said "I killed my father's son" and the other stuff
and no I seriously doubt someone would reach out to Fredo.. again. A man like Roth wouldn't risk going through it all again, he could tell Michael was suspicious or atleast had his doubts near the end
and I forgot to say Mike had his little seizure moment in the kitchen with Vincent, he was shouting "Fredo"