That will be an interesting question as the show goes on I think. I think as time goes on and they know who they are but are getting comfortable with their lives in Storybrooke I could see quite the conundrum shaping up if/when they have the opportunity to go back.
FTL didn’t look all that destroyed to me. I mean the castle was still standing. Sure the inside looked bad but the building was intact. I don’t think SB has to be destroyed to get back to FTL. And didn’t Jefferson, the Queen and Rumple all admit that FTL was still there?
All I know is that this parallel world stuff confuses the heck out of me on a good day. I do look forward to the inevitable “do we don’t we” decisions that will come if the characters en masse have the opportunity to go back.