I'm sorry, but the "you can't control those who want to leave anyway" is the exact same mindset my managers at work have. It's a poor excuse for poor management and leadership. If you go into all this treating/expecting top tier talent to be a one and done and/or chase more money, you're failing from the start IMO.
Sure, there are anomalies that are truly using a year or two as a stepping stone to bigger and better things, whether it be money, NHL/AHL deals, etc. but I'd like to think that isn't the norm for most players (certainly not disputing the change in landscape). If we are unable to retain talent that may have otherwise stayed due to personality, cultural, (you name it) issues, we need to look in the mirror and consider maybe we're the problem and not the player.
Not implying Maine has a problem just yet, however, I agree completely that we should absolutely be disappointed that we are/were unable to keep some of the players leaving this year especially if the reason for leaving is something that is/was within our control and/or capabilities to address.