I think that you might get more specific information through church channels from other LDS students and families who have been in this same position. A single gap year is common (although not for recruited athletes), but a two year gap is really only sought by LDS missionaries. Although he will certainly return with added socio-emotional maturity, the reality is that not playing his sport in a competitive atmosphere on a regular basis for two years could certainly adversely affect his level of play by the time he returns.
In any event, the coach really needs to know, and right away. I recommend that your son speak with the coach first, before proceeding. The coach was recruiting a team for this year, not for two years from now. Assuming that your son knew that he was going on a mission, it seems to me to have not been transparent with the coach, to have participated in the recruited athlete program, when your son likely knew that he was not going to be available to play for the next two years. Of course, if he had let the coaches know up front that he planned to go on a mission, and not be available to play until fall or '26, that’s a different story - but in that case, his coach would already have known, and you wouldn’t be asking this question.