I just finished the campaign on post human difficulty, which was bloody easy, and waited till the end of the credits and there's in fact an extra scene where the board of CELL are being hunted down by psycho, so yes somehow psycho survives, and the board are being evacuated by armed cell guard and they lock themselves in a room which psycho managed to get in, he then kills the armored guard and tells the board about the incident at the hospital where they ripped off his nano suit and said he'd like to file a complaint. and then it finishes there, so you can assume that CELL is finished with psycho killing the head board.