Maybe it's a choice. Either finishing playing this year, or have the surgery now and play next season. He needs to set his priorities. Playing at the D1 level trumps a juco career. He needs to prove himself on a bigger stage and do everything he can to get started on the right track.
OU will manage with Woodard and someone as the backup PG ..... maybe James or McGusty if Strong can't play. By playing, Darrion has the inside track to "own" the position the next year. If he has to sit out next season rehabbing, then a true freshman (e.g. Trae Young) may take the position and run with it the following year.
By playing next season he has a year to adapt to the job, and prove that he is capable of taking the reigns from Woodard after he graduates. Think how much better Walker is in his second year of playing. Strong can do the same.