No, he's signed on for Season 8 and Kiefer gave an interview where he even said he knows he's doing 8. Season 8 takes place 6 weeks after Season 7, and since the virus kills you in a day...there's no possible way Jack can be in season 8 if he's going to die. People are speculating he'll die in 8 though, I don't buy it.
I think Keifer said in an interview that Season 8 follows season 7 immediately. My understanding is that season 8 is the day after season 7. So, Jack may still be sick or dying. I do not think Jack will die in season 8, although I also believe that the producers/writers are still playing with various scenarios for the ending.