Assuming he won't sign a 1-2 year deal, I'd like to see a sign and trade.
As others have pointed out, Sullinger and Johnson both have good mid range games and could probably fill that role pretty well. Furthermore, both have assets that Bass doesn't have (Johnson, legit height; Sullinger, a legit post game).
If he signs a 3-4 year deal, how long will it be before one of them knocks him out of the rotation, destroying any value he has to the team?
And this isn't even counting the very real possibility that Green gets 10-20 mpg at the 4 spot, to further complicate the big man rotation.
If the C's could deal him for a big with a shorter deal who could be useful, I'd be all for it.