In Norse mythology, Thor (from Old Norse Þórr) is a hammer-wielding god associated with thunder, lightning, storms, oak trees, strength, the protection of mankind, and also hallowing, healing and fertility.
At one point, Neal Cassady was in Mr. Gold's "Cabinet of Doom" and could be seen standing next to Mjolnir, Thor's hammer.
There are many copies of Thor's hammer in the TV Universe, scattered across several dimensions. Should Thor - as played by Chris Hemsworth - ever appear on 'Marvel Agents Of SHIELD' (rather than just be mentioned) - the God of Thunder and his hammer Mjolnir would only be in the dimension of Comic Book Toobworld.
The Thor of the main Toobworld was seen in episodes of 'Hercules: The Legendary Journeys', and in a TV movie with the Hulk. That Thor looked differently from one production to the other can be attributed to the fact that the demi-gods from the Age of Legend - actually pan-dimensional aliens from a parallel world - had the ability to alter their appearance. Because of this, Thor could still appear in future TV shows and still be considered the Thunder God of Earth Prime-Time. (Unless, as I mentioned, it has anything to do with the Marvel movie franchise.)
Mjolnir, as seen in that aforementioned Cabinet of Doom, belongs to a Thor from yet another TV dimension - The Land Of Fiction, as seen in the 'Doctor Who' story "The Mind Robbers". It was assumed that the dimension faded away once the Doctor and his Companions were able to free Charles Hamilton from being the Master of the Land and the computer that enslaved hm was destroyed.
But the Land of Fiction was able to thrive on its own and so many more of Hamilton's imaginings never seen in "The Mind Robbers" flourished - Rumpelstiltskin, Peter Pan, Captain Hook, Pinocchio, Dr. Frankenstein.... To wit, most of the characters to be found in Storybrooke, Maine, for many of them found a way to cross over from the Land of Fiction and into Earth Prime-Time.
So should Thor ever appear in Storybrooke, he is a fictional construct given life from the Land of Fiction.
And then there's the Thor and Mjolnier of the Tooniverse.....
As for the Thor of the main Toobworld, at the moment his fate is unknown because Mjolnir has been spotted on several occasions without the Norse "god" present. Somehow it ended up in Warehouse 13 (along with Green Arrow's bow and the Penguin's umbrella.) But how the Warehouse agents were able to procure it for their archives is unknown. From there it was stolen by minions of Plutus the "god" of wealth so that he might put it on the auction block for other "deities" to bid on it.
I'm going to assume, unless proven otherwise, that eventually Thor will return to Earth Prime-Time. And he will have somehow reclaimed his hammer Mjolnir.......
'Once Upon A Time' - "Quite A Common Fairy"
'Doctor Who' - "The Mind Robbers"
"The Incredible Hulk Returns"
'Hercules: The Legendary Journeys' - "Norse By Norsevest"
'Warehouse 13' - "Mild Mannered"
'Supernatural' - "What's Up, Tiger Mommy?"
'Avengers: Earth's Mightiest Heroes'
'Marvel's Agents Of SHIELD'