Sonnen is also on the cusp of 36. It's not as though he'd be losing a title fight at 25 and saying, 'I quit'. Chael Sonnen has taken on all comers and was one of few men to offer to step in against a monster in Jon Jones on eight days notice. If that's not fighter's spirit then I don't know what is. The fact is, Sonnen has made a career out of being the company man and fighting the most dangerous guys. But he does want a belt, as all fighters should. If he fails against Jones, which even I imagine he will, his retiring at the age of 36, and after 15 years of MMA, hardly suggests he lacks a fighting spirit.
At that age, there's really no need to ride it out until 40 'just for fun'.
As to the original post, Chael Sonnen beats Dan Henderson easily. Jake Shields made Dan look like a novice on the ground. Henderson has literally zero ground game, and Sonnen would ride him to one of the easiest UDs of his career. Dan isn't difficult to take down, and Chael has a history of walking through big shots (minus the knee from hell).