LOL...small schools bring new situations to the game don't they? By rule, when a coach is beckoned on the floor the player is supposed to leave the game. However, I would imagine that NFHS did not consider the possibility that it might happen to a team that doesn't have a sub.
I think that I would let the player continue on. If the other coach protested and insisted on doing it by the letter of the law, I'd tell the player to go sit at the "X" in front of the scorer table and get them in on the next dead ball after the clock ran.
Z