Jones/Henderson has always been the fight that fell through that bummed me out the most. Probably as I had the poster up for years over my mini-fridge so was constantly reminded that it fell through lol.
But apart from the matchup, especially so as Henderson's knee injury that ruined it derailed the whole latter half of his career. His mobility was night and day different upon his return, you could immediately tell he hadn't returned to his prior form. And yet despite that he was still going to arguable splits with Machida, Rashad, Bisping, etc., and winning big fights.
I don't think he'd have beaten Jones, and we did eventually see them grapple and Jones subbed him, but man did that falling through have a ripple effect. Henderson could've possibly won the LHW belt, ended Jones dominance, then with functional knees beat a ton of other guys including winning the MW belt. When he's already a GOAT without all that.