I don't think Michael went to Sicily to avoid criminal prosecution. He was trying to escape a retaliatory hit.
While Vito talks at the meeting of the need to clear Michael of "all these false charges" the real message - and motivation for making peace - was to make it safe for Michael to come back without being assassinated.
It doesn't seem like any officials know of Michael's involvement until Cicci rats Michael out to the Senate committee.
Getting back to the original question, the Mafia code of the day probably meant that a wife and kids would not be targeted. So it's definitely possible that Michael still would have gone through with the hit, viewing the time away from his family as a necessary sacrifice to keep his father safe
It seems to me it was both “criminal prosecution” and “retaliatory hit”
Michael is a dead man either way by whoever gets to him first
If Tattaglia who is a pimp and Barzini the puppeteer hiding behind Tattaglia [presumably both would have known about Sollozzo-McCluskey-Michael meeting] still had the stomach! to take on the Corleones who had just gunned down a New York police captain, which has never been done before....
If Michael is identified as the Cop killer "Police Hunt Cop Killer" "City Cracks Down" No surprise - killed resisting arrest / trying to escape
I agree Woltz “the real message - and motivation for making peace - was to make it safe for Michael to come back without being assassinated”
Vito made the drug protection concessions from perceived weak position and things have also loosened up, all of which lulling other Dons into a false sense of security
1. no Sonny
2. Vito was sick
3. and Fredo -- well -- Fredo was -- well
4. Michael was not considered Mafia Don material nor threat
