Did not Nixon quit?
Yeah, what’s your point? It’s not as “ironic” as some people might think. It wasn’t as though he wasn’t coerced into resigning and as it turned out, he did do the right thing for the country by resigning.
Not really of his own volition. He hung in there until it was absolutely certain he was going to be impeached and removed from office, if he didn't leave first. He keep fighting until the last possible moment, even though it really caused a big deterioration in his health (which almost killed him after leaving office).
Most people in Nixon's humiliated situation would have simply hidden themselves away for the rest of their lives, but Nixon worked hard get back into a position of influence and importance (Monica Crowley wrote two good first-hand accounts of this). He refused to give up until the day he died, just like he kept coming back after the attempt of the Eisenhower people to oust him from the VP slot in '56, the loss to Kennedy in '60, the last press conference in '62, etc.