Moms always get a vote....
I'd go with celebrating Sr. day this year, if he is back next year to play no big deal, he can be the camera man for his buddies. Senior day with his class and having parents involved is pretty special.
My son was in similar position, he and his housemates missed graduation due to baseball, they had their own ceremony after playoffs , complete with caps and gowns, MC, music, etc. I think they had more fun doing that graduation walk than doing the actual thing. The video I saw was pretty amusing, lots of alcohol involved.