I think the book fleshes out that Sonny was ruled out because he has a wife and kids unlike Michael then but now if he is in the same boat No doubt dilemma!
Sollozzo only wants civilian Michael to proposition but really to buy time until he can finish Vito off
If he did kill Sol and Mac, would he need to go into hiding? exile option is not viable with Kay
Who is going to identify the son of the top Mafia Don
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.
