For a look at what the official interpretation of ROTJ's ending was back in 83, take a look at the last lines of the ROTJ novelization. It says "The Empire was dead. Long live the Alliance." There you have it.

It wasn't just the Marvel comics and everybody I knew who thought the empire was over, it was Lucasfilm, judging from that. And judging from the SE it was Lucas too.

It doesn't matter if logically the empire wouldn't be over just like that, Star Wars went for a simpler less realistic story. I've never been fond of the Star-Wars-is-for-kids argument, but it's true to some extent that the films were aimed at kids and having the empire just end like that is characteristic of the simpler storytelling you get in kids stuff.

The nature of the scenes at the end of ROTJ gives a clear emotional message that the war is over and the empire is done. If you get bogged down in the logic and try to think of Star Wars as if it was meant to be realistic then you'll blind yourself to that emotional message. Baronlando got it right -it's a fairytale ending. Star Wars is a fairytale, not realistic science fiction.

I think the 90s EU was aimed at an older age group than the films (or the Marvel comics) and they wanted to continue the conflict with the empire so they could have a story, so they brought in a revisionist take that the empire went on after ROTJ. But that's what it is -a revisionist take. Just like the prequels are a revisionist take. It's no more valid than the prequels nonsense.

In the original film, the intention is that the empire is over and that's the real story as far as I'm concerned.