Just for the record, real historians hate "what ifs", for good reasons
I suspect his fate would've been similar to Doenitz's. I don't see anything wrong with that. You can be as good a leader as you want to be, but if you're on the wrong side of the conflict, you have to take responsibility and pay the price, no excuses. It's part of the job, and Yamamoto knew as well as anyone - afaik he even acknowledged that.