Don’t get me wrong I love Mo Udall, he should have been President and could have been a great one—but 1976 was his year. Best case running in 1980 scenario? Have him keep it close with Carter in the primaries, very much the “if only we had picked Mo / too many liberals” thought—by 1980 the liberals do in fact consolidate around him and Mo is forced into it with no Kennedy and no Bayh.
Man I miss @Andrew T, so more importantly, how does popular culture change? (More intriguing thoughts at the link)
Here's the thing. Carter was still pretty obscure and losing to Ford would mean they'd go a safer bet and hence why we'd have Udall. That and 1976 was a poisoned chalice of an election year so whichever party got it was screwed.