I was in my early 20s in those days, and thought then (as I still do) that it was incredible the way group-think had seized the Nixon White House in that nobody, particularly the more seasoned members of the staff, stood up and said, in effect, "This is nuts. We have this election in the bag. McGovern is so far out there he's going to lose like Goldwater did in '64--and what do we stand to gain? Not one damn thing. And what if something goes wrong, especially if one of those bozos talks? No; call off this garbage. At worst we may not carry a couple of states apart from Massachusetts and the District, but so what?"
If someone had the guts to challenge the very notion of the break-in as high risk / low gain, it could have been stopped before it got started. Then Nixon's second term would have been more or less run of the mill until the Agnew scandal broke, at which point Spiro = zero. He'd get shitcanned so fast that if you blinked, you would have missed it. Jerry Ford gets named VP, but it's debatable he'd get the nod in '76.
If Nixon serves the full two terms by virtue of Watergate getting short-circuited, 1976 isn't necessarily a poisoned chalice: there would be no hangover. Much depends on whom the GOP nominates: Ford would be seen as a nice guy but of debatable executive material; Reagan might be viable but might not have quite enough to get over the top. Could be a compromise candidate, along the lines of a Howard Baker who would have had to have made a name for himself by some means other than Watergate.