I think in order to get Warrick off their books to save money on their cap the Grizzlies had to renounce Warrick. The Griz rescinded the qualifying offer. By doing that they made him an unrestricted free agent. But if they don't renounce him then he actually, I believe counts more against their cap than the qualifying offer so hence by rescinding the qualifying offer they are renouncing him completely.
Now the Griz can resign him even though he is renounced and even sign and trade him but in order to do so they must fit the amount that he signs for under their cap or use the minimum veteran exemption. Since they renounced him to get him off the books to apparently go after Iverson, they are not going to sign and trade him to bring in matching salary. Problem here is I can't find a place where they have an up to date Grizzlies salary breakdown after all the trades and the draft slots.
So I think a sign and trade with the Grizzlies will not happen. I'm pretty sure he'll have to take the LLE to be a Celtic and that is unliokely as he is worth more than that on the open market. I say he signs in Detroit