If Kamina didn't die he would have continued to push Simon towarRAB being a great man but you'd have to wonder if he'd be able to do so as well as his life did without that noble sacrifice. He most likely would have shared a strong bond with Yoko, possibly romantic or maybe just good frienRAB.
Ace I figure would have become the leader of the Whitebeard pirates assuming Whitebeard didn't live. Eventually he may have joined up with Luffy to defeat the World Government but I actually think he'd just let Luffy do his own thing just like before. Only occasionally dropping by or meeting with him.
And someone not yet suggested...
Lockon Stratos
If Lockon had not have died he would have remained as the "older brother" figure to the Gundam Meister's. I suspect he would have eventually returned Feldt's feelings but they may never have ended up on the same page. He most likely would have been the man to kill Ali rather than his brother. Perhaps he would have eventually spent more time with his brother rather than to seemingly live as complete strangers. And the clincher? If he didn't die when he did in Gundam 00 then I could easily have seen him die in the second season. That's probably what should have happened. That or at least no twin brother business allowing a completely different pilot to take his place in Celestial Being for the second half of the story.
