there's no one right answer or solution on the problem of when to leave. those with a good head on their shoulders and with the right people around them will be able to weigh the risks and rewards here. it is up to the program to continue to live up to the expectations so they continue to be an appealing destination to the player, their circle (agent, family, etc), and the team that holds his rights. and to make sure they recruit the type of kids who make those sound decisions
it's not a 1-1, but i know of a relevant case study from UConn. Sharks 2022 6th round pick Joey Muldowney could've left each of the last two years, especially when his twin/bestie/roomie Jake Richard decided to back out on returning for their senior season and signed in Buffalo mid-offseason. he didn't come in highly touted but when you end your sophomore season second in goals in the nation behind Ryan Leonard you can definitely believe your own hype. joey also has the size to deal with so that might make him more willing to stay and build strength to overcome it. perhaps the more interesting parallel here is how during his freshman year, uconn's dressing room allegedly was a train wreck and it showed on the ice. they had home goal scoring droughts that stretched multiple games, they had talent but it didn't go together, it looked a lot like BU last year. they lost a lot of guys to pros and the portal (Sergeev, Salminen, Wood), but the twins guilted Hudson Schandor into staying for his grad year, coach overhauled the roster, leaders established the culture quick, and the huskies of the past 3 seasons have emerged. injuries got in the way a bit last year but the difference in how the team felt to watch from 23-24 to each of the next 2 has been stark, both on the ice and just overall. i think it's made a big impression on all the players, because they haven't lost many to the portal since and are recruiting well.
in theory, BU should have an even easier time rebounding from a tough season due to the inherit recruiting and prestige bonus, and if they do it successfully a la 24-25 UConn, it can be spun into an "us against the world" rah rah thing that leads to some actual wins.