First, lets see how this season plays out. We're still ahead of where we were at this time last year, when we started the season 4-4. Remember, he took us to 8-8 after Sherman, followed by 13-3, 6-10 in an injury riddled season, followed by 11-5.
Next, I wouldn't fire him in the middle of the season, especially since we don't have anyone to fill in. We're still winning in our conference and there's still 11 games left to play. What I think should happen though is he should turn over offensive coordinator duties to someone else.
To be honest, I think next season will be his hot-seat season should we not make it out of the first round of the playoffs this season. I'm willing to give him one more go at it, but he needs to deliver.
As for a viable replacement, I'm not sure who is available and would be a good fit. We're not gonna get Cowher, so no one should even float that nonsense. If he goes anywhere, it'll probably be Carolina. Other than that, I dunno who else we nab. I know some people are gonna say we should get Gruden, but other than name recognition, I'm not sure why. Tampa Bay turned into a shell of itself during Gruden's tenure after winning the Super Bowl with a team largely built by Tony Dungy. Beyond that, I have no idea who would be both a good coach and a good fit.
Remember, the grass isn't always greener either. Things could be a LOT worse.