In the end of Avengers Thor returns to Asgard with Loki and cosmic cube. What if all this was a distraction and Thanos already invaded Asgard while all this was going on and took possession of the Infinity Gauntlet?
High chances are there that when Thor and Loki return to Asgard they'll find it destroyed. The same thing happened during a Thor's story where he and Jane Foster visit Asgard after some mission and they find everyone injured because Thanos and Mangog attacked to take possession of some artifacts that will give him power of the universe.
This has happened a lot of times in Thor's stories and even in Marvel Ultimate Alliance where Asgard failed in Thor's absence.
This doesn't mean that Thanos will be in Thor: The Dark World. The movie where we'll see Thor and Loki's adventure in other realms must be because of some other ties that happened behind Thor's knowledge.
What do you think?
Although Asgard's destruction is a big affair so we may see this in Movie's prologue or in a flashback sequence.