Well, in 1972, after the overwhelming defeat of the moderate Humphrey (many had expected him to do better due to the small margins in 1968), the Democratic party was kind of left without an identity. This can be seen in 1976 nominee George Wallace, who just 4 years ago had been a virulent racist but now preached civil rights after Arthur Bremer's shooting. However, his defeat against Ford once again left the party without an identity except vaguely liberal. It was actually somewhat a blessing in disguise that Democrats won in '72 and '76. Had McGovern been the candidates in either of those years, the hardcore liberalism of McGovernites would be discredited in the party and the democrats would probably default to Neo-Cons like Henry Jackson come 1980.
Most likely. Thankfully that it did happen. There was no way that the Democratic Party would have won in 1972 or 1976. Even with Watergate, people saw the Ford Administration, for what it was, as a somewhat stable ship. Along with the economic gains of the seventies, it was pretty much a foregone conclusion that Ford would get two terms. When people saw the more conservative and establishment Democrats get trounced in seventy-two and sixty-eight, the Democratic Party had no choice to turn to the McGovernites who were already pissed at Humphrey for taking "their" spot in 1972 and were pretty dismayed when McGovern lost against Wallace in 1976, surprisingly.
Either way, we really got lucky when after losing their identity more or less, the Democratic Party more or less turned to the liberal wing and on his third try, we had a McGovern landslide in 1980 after he beat Scoop Jackson in the primary. Although it did take a really long time to unseat the Republicans. They ran the country from 1969 up until 1981.
Who do you think would have gotten the nomination in 1976 if Wallace decided to not run? Would McGovern win the primaries or would the conservatives win the primary again? I think that the party would have probably defaulted to Scoop Jackson. But who knows?