I think we can safely say that the losing running mate from 1976 won't get the Democratic nomination in 1980. If the Democrats decide to go for their left rather than their center in 1980, Teddy gets the nomination, not Walter.
Unless a Democrat unexpectedly won the special election for the remainder of Dole's Senate term, Dole won't try to regain his Senate seat in 1980, so almost certainly he seeks the Republican nomination.
I wasn't trying for this, but assuming Anderson still tries his third-party run, I end up with the election ending up in Congress thanks to him taking enough votes from Dole to deny him Pennsylvania and Vermont. Kennedy wins the House, and likely the Democrats retain the Senate and thus the Vice Presidency as well.