I think he'll land a job elsewhere fairly easily (considering the situation). He has connects from his playing days, San Antonio days and now Boston.
And most importantly for him, he's a good coach. The fact that he hasn't been fired immediately suggests that he has enough goodwill to get another HC job when/if he gets fired.
He's not getting fired, he's just getting suspended (
which could potentially be for the entire season), and that'll likely mean the end for him, especially if the Celtics end up in a similar position as they did last season. His only saving grace is that they fail miserably without him and they'd almost be forced to bring him back on when his suspension is over.
But if whoever steps up in his place replicates what he's done (or the team improves), than they're unlikely to bring him back in that role. He'll either have to settle for a lesser position, or both parties will mutually go their separate ways. And while this might not seem like a serious matter, it's the nature of it which will give other franchises hesitancy to hire him in a head coaching role.