Set photos from Thor: Ragnarok leaked in August 2016 showing the original Odin on an Earth street corner (and dressed like a homeless person), so our general assumption is that he will play a significant role in the resolution of the story and the victory over Hela.
However, we do not really know how Odin will factor into the events of Ragnarok yet.
How that victory will specifically be achieved at the climax of the film remains to be seen.
Thor’s father (Anthony Hopkins) has played an instrumental role in both installments of the Thor franchise to date, and the reveal that Loki had somehow managed to dethrone him at the end of Thor: The Dark World was a perfect cliffhanger.