Our son broke his leg the fall of his senior season. He had signed a LOI and the coaches were planing on honoring their end of the deal no matter what. To make a long story short, my son chose to decommit and sought recruitment elsewhere and chose a JUCO over other offers.
Since he had been playing year round in Florida, he was known, so if his leg healed as anticipated, most programs were still interested in him.
He had to stay off his leg completely for 10 weeks as he broke his condyle. He worked very hard to get his strength up again and was able to play ball by Summer, which he did to get his skills back up before he reported to his JUCO in the fall.
It is amazing what happens to a leg over that time, be prepared for hard training to get it back in shape. My son went to a speed and strength coach who trained olympic and professional athletes.
Best of luck to your son, and you must be forthright. (I know that sounds odd after breaking a LOI).
And yes, I agree with all above, have your son make the call when he is able.