This is purely hypothetical, and am quite glad things didn't go this way, to say the least.
With that in mind, when hearing about Midway, it was apparently a rather luck driven event. The carriers were all opened up, for changing bombs apparently, when the US bombers arrived. If they had come only a few minutes later...
Basically, what would've the outcome been if they lost in Midway? Would we see a Japanese invasion of the US homeland? Doubtful, but still...