My first character never killed Caesar, but only because I never got round to visiting the Fort. I was NCR all the way and presumed I'd get a showdown with Caesar at Hoover Dam but that didn't happen, so I never actually met the guy 'till playthrough two.
Yep same thing here 100%

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Second play as Legion I met him, and let him die. He was an abomination of everything the Legion was built up to to my character. He used Tech... he was willing to use chems... he was weak, and none of his guards had the balls to finish him off, and take over, and to top it all off he was spreading lies about Lanius to keep himself safe. The Legion is better off without its archaic creator, and it is time someone led who actually believes in what he is talking about. Ahem >.>
3rd (as Yes man) dropped 8 packs of C4 outside his tent. Walked in they got mad and stormed me. Held out till all was around me at the door. Left the room, ran, counted to 3, and click... BOOM! Body parts went flying, and the left side of screen did not stop flashing crit/cripple messages for 5 minutes. Never did find a piece of Caesar though... dun dun dun...
4th... odds are high what ever Mr. House tells me to do.