Law School Finale Theories
First of all, I would like to apologize for not pushing through writing my analysis on the courtroom questioning of Joon Hwi in connection to Sol(AB)Hwi and the parallels between Prosecutor Jin and Prosecutor/Professor Seo. Might do them soon but no promises.
Anyway I deduced two theories based on this photo:
1. It's been a rough night, but gotta keep moving forward for tomorrow kind of scene.
2. Everything's done. They won. This is the last shot before we get to transition to the time skip, and it's beautifully done because they're all on the grass and it represents how tired and worn-out they all are. At the end of the day, even if they are legal adults, they're all still navigating growing up and maturity.
Anyway, I strongly doubt that this will be the last frame we'll see from the show. Shows tend to not want to spoil audiences so this photo being released means it's highly unlikely that we'll see this as the ultimate ending. To add, JTBC teased we'll be seeing some extra stuff from the squad so it won't make sense for their arcs to end without showing the future, I think.
EDIT: If this will be the final frame though, it could be during a reunion (but again, I really doubt that this will be the final frame).