My understanding was that J. Caleb Boggs was going to retire in 1972 but that Nixon, wanting to keep Pete du Pont in the House and prevent a likely GOP Senate primary between Du Pont and a former congressman, leaned on Boggs to run for one final term. Had Nixon stayed out of it, Du Pont would have been elected to the Senate in 1972. That would have meant that (i) Joe Biden may have never become a Senator but (ii) Du Pont would have never served as governor or Delaware; history certainly would have been very different.
But, yes, had Pete du Pont run against Biden in 1984, Biden would have been gone for good. Well, maybe Biden would have run against William Roth in 1988, but he probably would have lost then as well.
It also didn’t help matters to have the weak liberal RINO incumbent Governor, Russell Peterson, on the ticket. He went down to defeat (51-48%) to Democrat ex-Lt Gov. Sherman Tribbitt, in a year that no Republican should’ve had to sweat (he later switched to the Democrats in a fit of pique during the Clinton impeachment era). Tribbitt was later obliterated by duPont by a 14% margin in ‘76, when the latter ran for Governor (which to this day remains the worst defeat for an incumbent Governor in DE history).