He has zero leverage, the UFC will gladly let him walk rather than have Dana go back on his word. If anything they'd probably welcome it, Khabib isn't a draw, he's not a particularly entertaining fighter either. They'd rather let Conor have another shot at the title.
His corner is gone, Dana has said as much. The last person to sucker punch someone was Daley and we all know what happened there, I foresee his team being fired and him taking another fight in the UFC once it's all blown over. Money talks.