If RFK stays out, then LBJ is assured the Democratic nomination if he wants it. Assuming LBJ does want a second term, who wins in a LBJ-Nixon matchup? Period polling (pre-Tet) said LBJ.
I am convinced could die sooner than 1972. The stress of Vietnam and what was basically the Second American Civil war going on in the era probably took years off his life and hastened his death in the OTL; think of what it'll do if he still has to keep up with it.There's also the obvious point that, if Johnson wins, it's pretty much certain he dies at some point in his second (third?) term. IOTL, if I remember correctly, he died just a few days after his term would have ended, and add that with the stress of the Presidency, a close campaign, etc...
I am convinced could die sooner than 1972. The stress of Vietnam and what was basically the Second American Civil war going on in the era probably took years off his life and hastened his death in the OTL; think of what it'll do if he still has to keep up with it.