If there's sims on him, or anybody else with an offer, he'll just sign with other teams.
On the very last cycle of RS2, if any team offers the ship, no matter where they stand, the player will sign with them.
For an example, if a D2 or D3 comes in late and just offers the ship, but can't get to high or very high because of your effort, the player will still choose the D2/D3 because he WANTS to play ball.
If there is a school at moderate yes, a school at low yes, and a school at very low yes, he will accept the offer starting with the moderate team. If that team has no openings he'll sign with the low team. If that team has no openings he'll sign with the very low team.
I'm not sure the criteria of when a player goes juco instead. Maybe if there's NO offers? Not sure.