I have a hard time seeing the Warriors actually voiding the contract unless it was a career-threatening injury. Part of this is because if Ellis came back somewhere else and did well, it would infuriate their fans - but more important, it seems like it would be a lot tougher to attact free agents in the future. Harder to want to negotiate with them.
IMHO, they're posturing since Ellis and his agent are threatening (if they haven't already done it) to appeal the suspension. "Hey, go ahead and appeal - we'll just void the whole thing!" They're making it in everyone's best interest to take the suspension, rehab, and move ahead. If they did move to void his deal, there aren't that many teams out there who could offer him much of anything for a contract this year, so they've got a ton of leverage over him that way as well.