Vietnam What If: Diem not assasinated?

If Diem had not been assasinated, and let’s say, died of natural causes rather than murder, how would the Vietnam war played out? Would US troops of embarked on their mission to save the country from itself? Or would Diem of been more concerned at keeping them at a distance, whilst not denying his government of the aid and advisors (maybe air power) to defeat the Vietcong?

Diem was obviously unpopular, but he was regarded as the only anti-french ruler of South Vietnam who could hold South Vietnams factions together. So I was wondering, how would the war of played out if he hadn’t been removed? Would the war of lasted longer? Shorter? Or would it be the same end result?