Interesting topic - not something we had to deal with as scholarships were just year-to-year when our sons went through. Still, we had the conversation with the coach about subsequent years and in the end had to just trust them...or not? (We did and it worked out).
It seems to me, without the benefit of this experience with written vs. "promised" word, it will just boil down to trusting (or not) the coach's word. At this late date, it puts the player/parent in a difficult situation. I would've expected this to be explained to him at the time of his commitment, not now.