If he loses, he can leave. If he wins, he has to grant Chandler a rematch, and if he beats him again, he is also free to leave.
Basically, Bellator is banking on the idea that Chandler will beat him one out of two times.
I don't know why you are so against Rebney in this case. They matched the terms of UFC's deal word for word, as was their right, and Alvarez decided to whine about it and fight it instead of honoring the deal. He's actually lucky Bellator offered him this compromise, because there is a very good chance he was going to lose in court & that could have taken another year.