If his one year probabtion is up and they did not let him go then it seems to me that they intend to keep him. After all posting the job is just a "formality". Personally I would let it go.
If they have that many students that you are teaching the "over flow" then there may be a possibility that they could create another full time position. The Culinary Arts program at our local community college has a two year waiting list. They use to have two full time instructors. But, over the past several years they have added three additional full time positions.
Just something to think about.
" If a man is truly blessed, he returns home from fishing to the best catch of his life." Christopher Armour