Fishburne leaving just ain't gonna happen. Sounds like a whole lot of wishful thinking to me. Besides, they've already done the kill-off-a-major-character thing--Warrick.
I spend a lot of time trying to sniff out CSI news and rumors. I can't find a peep anywhere about the impending departure of anyone other than Catherine. Even if Laurence Fishburne hasn't renewed his contract yet, I suspect he's already made his intentions to renew known to the producers. While CSI is not the ratings juggernaut is was a few years ago (what show is after 11 seasons?) there's no indication that CBS is in anyway unhappy with the show's performance. CSI:LV is the only one of the three shows to keep its timeslot this year.
At this point, the only ways Laurence Fishburne would be canned in the near future are:
1) the ratings plummet into a black hole (which would probably result in the cancellation of the show entirely)
2) outrageous salary demands or special treatment (and everything I've read about him indicates that he's very easy to get along with and has a very good work ethic)
3) Charlie Sheen-esque off-camera behavior that jeopardizes the livlihoods of everyone associated with the show.
While I very much doubt that Catherine will be killed off in the Nate Haskell plotline, I could see some of the fallout of those events lead to her saying "Life's too short for this shit, I've got Sam Braun's money, I'm outta here." Catherine will likely either retreat into the casino world or pull a Grissom and move to academia.
At this point I'm almost certain that the show will be adding a new female lead next season as a direct replacement for Catherine (though not necessarily as supervisor.)
With Marg Helgenberger making only a few guest appearances and Jorja Fox seemingly unwilling to make a full season commitment anymore, a new strong female character is a must. Depending on Jorja Fox's involvement next year, it's possible we could see not one but two new female cast members.
While I agree that Nick is next in line to be supervisor, depending on how the whole Sqweegel/Haskell season finale goes, I could see Ecklie bypass all of the current regulars and bring in an outside hire as the new supervisor. That might be fuel for a new dynamic in the show - introduce a new boss who's perceived as a ladder-climber and too close to Ecklie and the other decision-makers, and less interested in being friends with the team.