I'm going to have to disagree on this one, because the entire Grissom/Sidle subplot now gets scrubbed, and that was one that's been a central part of the show since the first season.
Also, the competition subplot that's been dangled between Sara and Nick is gone.
AND besides that, I really liked both characters and the actor's approach to them. So I'd definitely say no recasting, just bring in the new characters, or don't even do that, bump Greg up to full time CSI status, and make Grissom and Catherine the main team, with Greg and Warrick the B team and put some new blood in as one of the lab techs.
But this really, really stinks as a big fan of the show, since all the actors had great chemistry.
God, I feel like SUCH a fanboy.