Why would he? He's established himself as a starter, he's relatively young, and he's still got a couple of more contracts to play for. My guess is that he'd do better for himself being either a starter on this team, or the lead guard on another team. Taking a subservient role this early in his career isn't maximizing his earning potential.
So like I said, if you're going to have him come off the bench, your gambling that he'd be OK with that. I think that's unlikely, but who knows? To me, the most logical way to make sure you get an outcome you can live with is figure out a way to make it work with Damian in the starting lineup. If you can't do that, then trade him. If you can't get decent value in a trade, then broach the subject of trying juggle his role and try to bring him off the bench as a last resort.