In order to return midseason, Thornton needs to make the opening 53, then be moved to IR. And I expect that he will, unless his injury really is a season ender. Here's my guess at the roster:
QB (2): Mac Jones, Bailey Zappe (Practice squad: Trace McSorley, Malik Cunningham)
Cunningham's inability to do anything at receiver combined with the limited look he got at QB tells me that even if the Pats still like him, he's not ready yet and the Pats will try to slide him through to the PS. Based on Zappe's awful preseason, if you are the Pats you might be looking to add another QB though. If not, McSorley hangs around as injury insurance.
RB (4): Rhamondre Stevenson, Zeke Elliott, JJ Taylor, Kevin Harris (Practice squad: Pierre Strong)
Harris and Strong have done little to nothing, but with Elliott and Stevenson able to do some 3rd down back stuff, Harris gets the nod as the 4th guy. Taylor flashed, and may get 3rd down back snaps. Montgomery is too brittle. CJ Marable never got to play, even in the last preseason game.
TE (3): Hunter Henry, Mike Gesicki, Matt Sokol (Practice squad: Anthony Firkser)
Gesicki is really a big WR, so there needs to be a 3rd TE who can block, and that is Sokol. Firkser showed well in camp, and the Pats are thin in real TEs, so he may stick around. Maybe Scotty Washington also sticks on the PS? Lumpkin will be cut.
WR (6): Davante Parker, Juju Smith-Schuster, Kendrick Bourne, Demario Douglas, Tyquan Thornton, Kayshon Boutte (Practice squad: Thyrick Pitts)
Thornton likely makes the team in Week 1 and then immediately goes on IR.
OL (9): David Andrews, Cole Strange, Mike Onwenu, Trent Brown, Riley Reiff, Jake Andrews, Antonio Mafi, Sidy Sow, Conor McDermott (Practice squad: one of Ferentz, Hines, Murray, but I think they will want to look outside the organization for a practice squad OL or two) NFI (1): Calvin Anderson
NFI is one of those deals where, once the player is ready to return, a clock starts and the team has X weeks to active or IR him, right? One of the original 9, probably Reiff or McDermott, will go when/if he gets back.
Edge (5): Judon, Wise, White, Uche, Jennings (Practice squad: Perkins)
Not much to say about this group. Perkins flashed a little yesterday, but it was his first action of the preseason. Not enough.
DT (5): Lawrence Guy, Christian Barmore, Davon Godchaux, Carl Davis, Sam Roberts (Practice squad: Jeremiah Pharms)
I have Roberts making it over Ekuale. The Pats would welcome whichever one of them is cut to the practice squad... but I think either one will be claimed by someone.
LB (5): Ja'Whaun Bentley, Jahlani Tavai, Marte Mapu, Chris Board, Calvin Munson (Practice squad: Diego Fagot)
Mack Wilson gets beat out by Munson.
CB (5): Christian Gonzalez, Jonathan Jones, Jack Jones, Marcus Jones, Myles Bryant (season ending IR: Isaish Bolden) (Practice squad: Ameer Speed)
S (4): Adrian Phillips, Kyle Dugger, Jabrill Peppers, Jalen Mills (Practice squad: Joshua Bledsoe)
ST (5): Chad Ryland, Bryce Baringer, Joe Cardona, Matthew Slater, Brendan Schooler (PUP: Cody Davis)