The 1972 election was probably unwinnable for the Democrats, but they didn't have to lose 49 states. What would the result be if Humphrey and Nixon re-matched?
I'm not convinced it was unwinnable. I think 1972, much like 2016, was a year the Democrats lost a winnable race. Hubert Humphrey probably wasn't the strongest candidate, but he would have had a far better chance than McGovern. I think Americans liked McGovern personally, but viewed him as a far-left ideologue. Humphrey would not have been viewed as far-left, but he couldn't be the true anti-war candidate given his administration continued the war.
If the trends of 1970-71 continued into '72 (polls in I think it was early to mid 71 showed Nixon was vulnerable), the dems MIGHT'VE had a shot, although I'd personally give Nixon the edge. By 1972 (and especially after McGovern won the nomination), that wasn't the case and Nixon had as much of a lock on the race as Reagan had in '84.