And Caesar's Legion can exist easily with Caesar dead..
I agree that Caesar being alive has little to do with the story but I disagree with the the above line.
I forgot who said it, but I agree with what a npc said.
That Caesar's Legion are gathered around his personality and not his ideals. As soon as he is dead, human nature will take its course. Greed, Ambition, etc. will tear it down in decades.
But I think that is out of the scope of Fallout New Vegas.