Morrisville, Brockport, and Buffalo all max out at 18 points if they were to win out at this point (and Brockport and Buffalo cannot both win out anyway, since they play each other next week). Geneseo can rise to 22 points (Plattsburgh's current total), and Potsdam can get to 20 points.
Thus, sitting at 19 points, Oswego can fall no further than 4th place. Geneseo can still get to a tie for 1st place in the SUNYAC (Plattsburgh loses out, and Oswego loses to everybody but Plattsburgh), and Plattsburgh can fall no further than a tie for 2nd with Genseo (but can fall to 3rd on tiebreakers, I believe).