A friend of mine actually suggested that in a few thousand years a future civilization will believe that Superman was a god we worshipped. This would make sense given his history and how close to mythology he is based. I don't think people will be still following new adventures of him but I do think he will be known as a mythic figure.
I keep picturing a scene similiar to that one in an episode of
Star Trek TNG when the Enterprise finds a frozen capsule of people from the 20th century and unfreezes them. 400-500 years from now, some unfrozen person from our era will be going through a star ship data base looking for old episodes of
Superman. In between trips to the holodeck for some of that sweet, sweet Holoporn of course!