In the comics, Ragnarok was brought on when Loki freed Surtur and various other enemies of Asgard. The evil army went on to attack the realm and the war began. With Loki on Asgard's throne at the moment, expect him to do the exact same thing to rid the realm of those people who oppose him - Heimdall, Sif, the Warriors Three etc - and, when they find themselves in trouble, he will then smugly reveal himself as being alive and as having posed as Odin since the events of Thor: The Dark World. When it all gets out of control, he may well end up being the one who resurrects Thor after his almost inevitable (first) death in Avengers: Age of Ultron. Regardless, there's no way Loki will spend this film posing as his adopted father. He'll want the glory of causing Ragnarok (at least until it inevitably puts his own life at risk) and that's great news for fans of Tom Hiddleston.
