Thor 3 Will Follow Avengers 2 End Closely
Loki will come back to witness the dusk of the Gods.
The Scarlet Witch will use her power to show what happened to Asgard. Which will make Thor eager to save his hometown. While what role will loki play is unknown to us till now. However, in the end of Thor 2, Loki disgusted as Odin, so, we can speculate Loki will play a catalyst role in the story. Loki has always been a very important role in Marvel series movies, although he is not a leading character. The CEO also indicated that Loki will appear in the two sections of Avengers 3 due to the unlimited gem in his wand.
In a word, the main plots of Thor 3 are supposed to focus Asgard collapse or even the death of Thor and Loki.