Lisebergbanan is now running again, but from now on with only 4 trains as the 5th train that rolled back was too badly damaged and could not be repaired.
The official cause of the accident according to Lisebergs own investigation was that a bolt in the chain unscrewed itself and the chain separated. The rollback dogs on the trains were coated with a low fricton material similar to teflon in order to reduce noise and that was why the train slipped of the anti-rollback "teeth". This material has been removed from the trains. They were worried this would increase the noise too much, but apparently it only increased marginally.
Also, they've will inspect the chain more often. Before it was only inspected once a year, before the park opened for the season.
The source of this is the local morning newspaper, Goteborgs Posten. AFAIK, the article was only in the printed paper.