We've been tracking this in a few threads, but I wanted to create a new one devoted to the subject in case there are any questions/thoughts.
The Celtics signed 5 players to rest-of-season/multi-season deals -- Hauser, Kornet, Stauskas, Fitts, and Morgan. Each of the 5 have different contracts, and from those contracts we can make some assumptions as to which are mostly likely to return to the Celtics next year. The contract status of each is as follows:
Hauser -- Team option for next season, $300k guaranteed if exercised.
Kornet -- Rest of season only. Free agent next season.
Stauskas -- Next season fully guarantees on July 15th, non-guaranteed before then.
Fitts -- Next season is $50k guaranteed if he's not released by September 1st.
Morgan -- Next season is completely unguaranteed apparently (I wouldn't be surprised if ultimately we find there's a guarantee that's similar to Fitts' $50k).
Accordingly we see the C's value Hauser the most, as they're willing to make the decision about him the earliest (before free agency). This is confirmed by his placement in the rotation, and also what we've seen from him on the court. He's not a lock to return next year, but as of now it's more likely than not he'll be back.
Stauskas' contract is one that shows he had to earn his roster spot next year over the final month of the regular season and for as long as the postseason lasts. While the C's technically have the most active part of the free agency period to make the decision, they won't have much more info on Stauskas. In my opinion, his poorly timed ankle injury that kept him out the last two weeks when there were occasionally minutes available has doomed him, barring something completely unexpected occurring in the postseason. This disappoints me personally, as I've long been a Stauskas fan, but he's highly unlikely to be kept beyond July 15th.
Fitts seems to be next in the pecking order, with a small guarantee on September 1st. I expect him to be on the C's summer league roster. Depending how tax conscious the Celtics are, they might release him before September 1st if they already have 15 guaranteed salaries, and don't even want to pay him the $50k to show at training camp, but otherwise I expect him to be with the team in October with a chance to make the roster.
Morgan has no guarantee, which means everything I've said about Fitts is true of Morgan (summer league, training camp), except he's even more likely to be on the team in October, since there are no tax consequences for the C's. Because of Fitts' guarantee, I'd say Morgan has a slightly better chance of being in camp, but a worse chance of making the roster.
Kornet is not under contract for next season, and so will be a free agent. Accordingly, he's the least likely to be on the team next year.