Maria's one of the best things about RAW.
I think if Tazz moves to ECW (the article up on WWE might suggest that he will) then they should replace him with someone different. If Cornette was still around, I would have suggested him, but he's in TNA now. Heyman or Al Snow would have been good choices, but they're both busy with ECW. To be honest, I can't think of anyone within the company that would fit in as a colour guy on SmackDown!
That said, Tazz can't (and won't) wrestle, and Joey was used to doing commentary alone, so maybe he'll just stay on SmackDown. He and Cole work well together.