Vito was or at least later pretended to be somewhat ambivalent about Michael's entry into the criminal world and his subsequent ascension to acting Don.

I think Vito recognized that Michael would have been a better Don than Sonny but Michael had other talents which Sonny lacked, which would have made Michael a perfect bridge to the outside world or even more or less completely legitimate. And that is what in different ways, both Vito and Michael wanted.

If Sonny had survived Michael would not have felt obligated to take over the family business.

So I think the crown would have passed to Sonny. Michael would have been free to pursue a political or business career, no doubt aided by his family's influence. Ultimately it might have ended up something like the relationship between the brothers in the Prizzi's Honor novel, in which the older brother had the Mafia muscle and formal authority but the younger brother had the financial acumen and political/business ties.

I think both Michael and Sonny respected each other, which wouldn't have been the case with Fredo in the mix, so despite a few arguments and insults over the years I think this would have have been a stable and profitable relationship. Each of them gets to do what they're good at. Sonny runs the crews and plays tough guy; Michael uses his intellect and launders/invests money-provides political cover.

Great answer and its hard to disagree with any of it.

How easy would it have been for Micheal to return to America, having commited double murder already and seen his wife blown up, an continue as a 'normal' citizen?

I think theres evidence to suggest that Micheal knew when he first said goodbye to Kay that he was going to join family business and that once he got involved in the Mac and Sol situation that there was no other route for him to take.

See, I think that's where my interpretation is a little different. I don't think Michael wanted the top spot, at least not while Sonny was alive. I think a lot of Michael's bile and anger in the second film (and a little in the first) comes from the fact that he felt trapped by obligation, love and pride into his role.

My take is that the Michael character feels "Oh so my destiny is to be a mob boss, huh. Ok, I'm going to be the meanest, deadliest greediest, coldest mob boss that ever existed! How you like them apples!!!" He's on a multi-decade temper tantrum against events that happened and decisions he made (that he later regretted).

But anyway, assuming for the sake of argument that Michael stayed involved in the operations end once he returned, I still don't see Vito giving him the nod. I think Vito would have had other plans for him.

I think Vito was always a little leery of Sonny's leadership abilities and wisdom and to use a phrase from Puzo, Sonny's (excessively) violent prosecution of the war would only have "confirmed his judgment". A Don shouldn't regularly lose his temper, make enemies unnecessarily or get caught not thinking. Remember in book, Tom is surprised that Sonny evidently thought his thing with Lucy was secret.

Again, though Sonny was the oldest, a huge asset to both his father and the Family and Sonny wanted the job. I think Vito would have given it to him despite his misgivings.

Another thing is that there is no evident jealousy/bitterness between Sonny and Tom or between Sonny and Michael as there was between Tom and Michael so with Vito and Tom acting as Sonny's brain trust until Vito's death I think Sonny might have managed to be a passable boss. He wouldn't have been as smart/detailed/cold as Michael but Michael could/would be doing other things that would bring in even more $$$/power. Michael can do Sonny's job but Sonny couldn't do what Michael could.

Also, out of curiousity, what is the evident jealousy between Tom and Micheal that you refer to? I can see it too in a way but I'd like to know what led you to that conclusion and see if they are the same factors that made me consider this.

I think theres evidence to suggest that Micheal knew when he first said goodbye to Kay that he was going to join family business ...

I think that Michael was jealous of the close relationships that Tom had with Vito and Sonny. I also think he blamed Tom, rightly or wrongly, for Sonny's death. And from flashback at end of 2, Michael didn't appreciate Tom discussing Michael's life with "their" father.

So when Michael took over he was a little colder to Tom than needed to be-putting Tom on the constant defensive- which allowed Michael to manipulate him more. I buy that Tom had to try to remain on good terms with someone who obviously had no problems having him murdered if it came to that.

I'm not sure that Tom, who had already and been accepted as a full brother/son by all of the other Corleones, would have been so needy of Michael's approval on a personal level.

When he visits Kay, he decides, that the situation has become too dangerous for her.

* The look on Tom's face when Micheal mentions his plan to kill Sol and Mac, everyone else laughs it off but Tom seems concerned/wary

The relationships between all the brothers is fascinating. Jealousy, one-upmanship, bitterness all combined whilst fighting for thier fathers approval. One of Vito's greatest challenges must have been to manage the relationships between his children, whilst being head of the most powerful mafia family.

Why would it have been dangerous for Kay? It's a common rule in the mafia not to hurt wives or civilians.

I think he just wanted to keep to himself for the time being to sort things out. He didn't want to put the burden on her shoulders by involving her in the situation.

I think Tom was more concerned (from a consigliere's perspective) about what the result would be and the implicated risks it would bring to murder Sollozzo and a police captain.

I do think, however, there is an element of danger that he wanted her to protect her from. Though wives and civilians were not targeted it doesn't stop them from getting hurt occassionally, wether intentionally or not, see Appollonia and Micheal having his face broken.