No one.
While I’m not completely satisfied with the current incarnation of history, I can see where things might have been worse if people who were killed were not. So much worse, in fact, that we may not be alive to discuss “what if” had things not occurred in the manner that they did.
Some examples:
Abraham Lincoln - Would have still had to get his measures through a Congress with whom he rarely agreed.May have had Marfan’s Syndrome meaning that his life would have been shortened anyway
Lee Oswald - While he may have “cleared up” whether or not his actions were part of a conspiracy, he may have gone to the electric chair still proclaiming his innocence. The conspirator crowd would still have a hook to hang their tinfoil hats upon.
MLK - Was fading in influence in the civil rights movement as many urban Black Americans saw that non-violence was not achieving their goals rapidly enough. May have been marginalized as the majority of his compatriots were after the 1960s.
RFK - While he might have beaten Humphrey, who’s to say that he would have overcome the Nixon juggernaut in 1968 or 1972. May have had to settle for 1976 or even never had a shot at the presidency.
One of the few assassinations that I might want to see “walked back” were the murders of Rwandan President Juvénal Habyarimana and Burundian President Cyprien Ntaryamira in 1994. Their deaths, which occurred when their private jet was downed by a missile, led directly to the bloodshed in Rwanda in 1994-1995 and indirectly to the war in the Congo that is still raging to this day. Millions died unnecessarily because of these two men’s deaths who might have had to and Sub-Saharan Africa has been in turmoil ever since.
Now I have to think of a real answer…