Logical Solution: Albert works to make a consensus-based government, with mixed effectiveness. South Vietnam falls because no, the American people are interested in going back, and while you can't appease the Far Left and Far Right, you can get a steady-as-she-goes government working with members of both parties, which would be necessary after the crisis.
There would be legal issues, over the Presidential Succession Act, since its on shaky constitutional grounds, that would define the domestic politics of the era. America would for practical purposes be listless in the era of collapsing expectations that the 1970's were, economically we're probably worse off come 1976, the malaise is even greater. Odds are Reagan wins in 1976. Though Carter is most certainly not the Democratic nominee, depending on who you have, the Democrats are not without any hope.
Theoretically we can argue the West Wing option would work, with an Election of 1974, depending on how the Succession Act arguments work. Reagan still probably the odds on winner in that case.
Long Term, the 1970's are worse for the West then they were IOTL, a Reagan hardliner government from 1977-1981 will IMO not be a good thing, but its not a world-collapsing thing. Theoretically the timeline can go with the "Kill all the Asian People" cliche that we so often see in China, we could see bad juju hit Europe or Russia, but at the end of the day I don't think the collapse of the New Deal Coalition will lead to Corporate-Fascism that we saw in the proper timeline.
Gumboverse Solution: Acting President Carl Albert is as IOTL an Alcoholic. Inevitably in the bad juju universe of the timeline he will kill someone, as he almost did on September 11th 1972 in a Drunk Driving accident. Or he'll be a Disney-in-AWOLAWOT, foggily leading the nation to ruin as he listens to the worst of his advisors and tries to avoid dealing with the crisises at hand. The CIA and FBI go out of control instead of being brought to heal, Leftist Terrorism and Rightist Militia movement shit starts up, Howard Hughes still magically decides to create Fox News early, the world goes to shit. Albert deploys tons of draftees to Vietnam, but poorly, the United states falls into its pit of warfare and horror.
In 1976 Albert stands down, and Lester Maddox is the Democratic Nominee and James H. Madole wins the Republican nomination and the White House.