I have seen the special that shows the 4 missing years from the season finale...(SPOILERS)Michael is not dead. He has gone back to the doctors from the company which still exists although the general is dead. They performed additional surgery in return for his commitment to work for them. After the success of the surgery he faked his death with the help of Kellerman and the US government after agreeing to help them bring the company to its knees. Other stories with the other characters' lives mix into the show. The visit to the grave was only to commemorate his success at tricking the company into believing he was dead and ending its reign.