If Bynum is traded, it will probably be for someone making $2-2.5 million. That player will likely be released, and Danny will just trim a few hundred thousand off of his luxury tax number. Any trade exception will be negligible, and there's no draft pick coming our way.
More than likely he's just released.
For example, perhaps the Nuggets would take Bynum for Nate Robinson, who's still recovering from an ACL. Such a trade would save the Celtics $800k, and cost the Nuggets the same. Nate would then be waived by the C's.