This same type of cautious thinking cost us Walsh too - who, if not for a twist of fate and lucky break, may have never returned.
He had similarly never 'proven anything' or 'forced his way into the team' and was being told 'his time will come' while we persisted with an average option who had no future in the team. Players are going to do what's right for them and pretending it's still yesteryear where players honour their contracts and being blind to the reality isn't going to help.... We don't have 2 grand final appearances and a premiership if he doesn't come back.
It's as much as the club's responsibility to guide and develop and put these players in a position to succeed as it is the player's responsibility to earn that spot.
If we think Mozer is the future of our team at the most important position in the modern game, I'd personally rather go slightly early and at least play a hand than die wondering and see him leave without ever having the chance.
Give him his shot, if he sinks then he sinks. If he swims, we're far better off both in the immediate and long term.