Thomas is a good but not great player on a great contract. He's one of the few guys we have who'd make a very useful piece in acquiring a great player. I'm sure we'd be happy to keep him if we can but realistically he's more likely to be shipped off if we have a chance to make the big deal we're angling toward.
How valuable is Thomas as a trade piece, really? At the deadline this past year, he was worth an expiring and a late 1st. Part of the valuation of him at that time was the fact that two teams in the span of a year had decided to move on from him, apparently due to questions about his defense and willingness to play in a supporting / bench role.
If Thomas continues to succeed with the Celtics, his value might rise somewhat, but do you think other teams will really see him much differently than they did at the deadline this past season, or last off-season?
I think Thomas is what he is, and though his contract is arguably a great value, I think it also represents the value the league places on him. Useful in the right situation, but volatile and perhaps not content to the play the role for which he is best suited on a good team. He's happy with the Celtics now because he's the undisputed #1 option. A team that might trade for him probably won't be looking to use him that way.
I think he increased his value last year.
For one, his productivity on the C's was significantly higher than his previous. His per-36 scoring and assists were 26.4/7.5 with the same efficiency (compared to his recent averages of around 22/6). Say what you want about his defense but offensively those are elite (the only other guys who put up per-36 numbers like that are Curry, Harden, Durant, Westbrook and Lebron)
PER, win shares and OBPM were up. Small sample, etc. but the numbers are pretty amazing for a 20-game stretch.
Second, he did that as the #1 option, which he hadn't really done before.
I'm not sure how much these things would matter to a trade partner, but I think he's more valuable now than he was before we acquired him.