The logical thing to do this offseason is to make a run at a premier free agent, a la Hayward (even if you need to give up some combinataion of Olynyk/Crowder/Bradley to clear enough space), and then run it back one more time in IT's final contract year.
Then at the end of the 2017/18 season, you can decide whether or not you want to sign IT. The worst case scenario is that he walks for more money. But in that case hopefully you've added someone to pick up the scoring slack, in the form of Hayward, or maybe the guy we draft this summer, or maybe someone like Jaylen Brown makes the leap.
Trading him this summer makes no sense. First of all, you've proven already this year that you can win at a very high level with IT as your starting point guard. You're not that far away from contending (heck, the computer models give us a 4% chance to win it all THIS YEAR). Second, though Ainge has traded away superstars before, you can't trade them when you're pursuing free agents, a process that IT will no doubt be playing a significant role. Third, as many have already mentioned, you're probably not gonna get much back in return for one year of IT.