Well, I think he is alive based on the way the anime left it. I don't know if it was different in the manga.

But, because they purposely hid the the face of the person driving the carriage and then when CC said "isn't that right, Lelouch?" she kind of looked in the direction of the driver. So that leads me to believe that it was him and she was speaking directly to him, not just thinking out loud.

That isn't to say he wasn't really stabbed by Suzaku, but that he was immortal at that point having killed Charles in the other realm and gaining his immortality.