Not exactly news, but this is confirmation of what we all expected to be the case.  From Jeff Howe of The Metro:

While Cassell’s days in Boston are likely done, [PJ] Brown told Metro he hasn’t ruled out a return. The belief is he’d once again wait until the second half of the season if that’s the case.

So we'll get a chance to see how Patrick O'Bryant is working out, not to mention any trade talk through the deadline.  Then if nothing else shapes up, we can take another late season pickup with PJ.  Of course he'll be a free agent and he can chose whatever team he likes.  But his positive experience last year might sway him to stick with Boston.  Again, someone will need to be cut, but by that time in the season, the spot will already be open or the choice of who to cut will be pretty clear.