The mob's long standing rule of "once you're in, there's no getting out", applies to it's made members, not it's associates.
but....the novel does briefly mention Michael having a 'made' ceremony of sorts after the Sollozo shooting. Seems to me that associates would especially have to take the vow b/c they could bring the whole operation down if they ever turned state. And I don't think Vito could have pulled Mike out of the family after Sicily b/c as Don Tomassino says ...
'your enemies know you're here.' There were enough ppl who knew that Mike was involved, enough ppl that knew Mike had pulled the trigger and was now 'one of them.' I don't think it would sit too well w/ the other dons if Mike decided to 'dangle his toes in the water' and then leave.
I don't think there's any doubt that Mike's lust for revenge made it impossible to leave the life. But I don't see how someone could get in as far as he did, and then just duck out. As far as handing the operation over to Tessio/Clemenza, I've posed this question in yrs past, and always gotten the impression that this was not possible. Someone in the Corleone family would have to be in charge, probably as a matter etiquette. If it was possible to hand over the operation to Clemenza/Tessio then why didn't Vito do this from the start?
Why not save Mike the anguish and then simply let him go on to be Senator Corleone while Tessio runs the family? Plus, concerning Mike's possible 'exit' from the family, after killing Sollozo Mike would have probably been safer as a made member. If he becomes a civilian he is perhaps even more vulnerable to a revenge attack.
As soon as Mike kills Sollozo and McCluskey I think his fate is sealed. He is in. Perhaps if his involvement had not been so hands on it could have been different. But he was just too far in to ever leave IMO. His chance to 'leave' would have been the world of legalized gambling, etc. Here he could have still been a Don but would not have had to deal w/ the day to day trials of being a mob boss.
