I don't understand why Mitchell would want to leave Sydney, unless he sees too many good Academy players coming through. Sydney are paying him well enough. He gets to play in a strong team, manages to play consistent finals footy and has a reasonable chance of being in a premiership team. It is his Old Man's club. That sounds like some good reasons to stay.
If he decides to go, Hawthorn would have to come up with the sort of deal that would get O'Meara. I can't see them managing it. They don't have enough good players who want to leave or any draft picks that Sydney would want.