Hilarie Burton exited the show after Season 6, Janneel Ackles’ recurring stint ended in Season 7, and Antwon Tanner recurred for just five episodes in that final season.
It probably wouldn’t be the most direct follow-up, considering only Robert Buckley was a series regular in Season 9.
But hey, what are reunions for if not catching up with people we haven’t seen in a long time?
For this to be a properly sizable One Tree Hill reunion, the mystery project would probably need quite a few more cast members involved. although something could still be done with just these four.