Actually, I've been thinking about this lately, and as much as I hate to say it, Scoop Jackson would've been well-positioned in 1980, in this scenario, given the Iranian hostage crisis and the recession. He'd be able to run as economically left-of-center, but as a Mid-east expert and defense hawk who could "stick it" to the Iranians and the Soviets and "protect Israel." I'd hope for it to be someone like Mondale, Bayh, or Church though. Mo Udall had too many health concerns by this point, and probably wouldn't have run. The Republicans would've had a Reagan vs. Dole fight, presumably. This would be a really interesting election.
If Scoop Jackson were to be elected in 1980, it would not have turned out too well. He probably would have went to war with Iran over the hostage crisis, made the inflation problems worse due to his stimulus programs and might have even intervened in the Soviet-Afghan war. The Republicans might have been able to make strong gains in the 1982 midterms due to Jackson's policies. If he lived past 1983, he might have been defeated for re-election in 1984 by either Bob Dole, Howard Baker, Mark Hatfield or even Ronald Reagan, although Reagan would have been 73 and was beginning to show signs of Alzheimer's by 1984.
I agree that Lloyd Bentsen, Ted Kennedy, Walter Mondale, Birch Bayh, Frank Church or even Jimmy Carter again would have been much better choices for the Democrats in 1980 if Ford was re-elected.