I'm not simply because I think Diaz is starting to hate MMA. He's definitely a contender if he chooses to return.
It's the UFC he hates. He's started to feel like Fedor with no Pride or Strikeforce to keep him amused. He was planning on doing pro boxing before UFC if I'm right, but they handed him the title shot to bring him over.
Things could go downhill big time for Diaz. He was over MMA, and got brought over for a Welterweight Title fight in a promotion he wasn't really interested in. He didn't turn up to a press conference and got taken out of the fight. He destroys his opponent and gets the title shot. The champion is pulled out due to injury. His replacement uses avoidance tactics and won't engage Vs Diaz. He is then banned for a year for having marajuana in his sytem.
That's A LOT of stuff to piss him off. Wether his fault or not you can understand why he might be sour. He has now called out the greatest fighter in the world, in a non title fight, who showed interested in the fight too. The owner of the company has comdemned the idea, and in the wake of the suspension (and his own personal dislike), he will probably stick to the rules and make Diaz have another 3 fights before he gets the title shot (which is fair). Diaz will still feel like he was robbed, twice, of his title shot (wether he was or not) and everything will be getting him down.
I won't be surprised to see him lose another fight in the UFC (by lay and pray or avoidance tactics), quit the company, have a fighter or two in One FC and then retire, only coming back to stand behind his brother (the lightweight champion
Would suck but...