I am not idolizing anybody. The fact is that Roy was the main driver on his line and on his team this year. That being said, good players need to play with good players, it is true for Roy as for any good player. My point is that Roy is not the product of playing with Xavier Parent.
Next year Roy will play in a weaker league relative to himself. I mean that all the 20 years old and many good 19 years old players will be gone. So yes he will lose his two good 20 years old linemates, but the same will happen on every team. The Bourque, Bourgault, Lapierre, Dufour, Nadeau, etc... will graduate in the AHL or NHL and many other 19 years old players that won't play next year as 20 years old will also leave the league.
Next year he should produce at a similar rate, and if a younger players like Ethan Gautier takes a big step and his team could also trade to acquire another 20 years old to play with him, Sherbrooke will want to maximize their window next year. That being said, one need to be careful with points total. Nick Suzuki got three similar seasons based on points/game in the OHL from 17 to 19 years old, but he improved nonetheless as a player. So if next year Roy is again around 120 points, it will not mean he did not improve.