I also had this same theory…. I THINK SOME HOW THE APPLE TREE IS THE SEAT OF REGINA’S POWER…. KILL THE TREE AND YOU DESTROY HER POWER…. CURSE BROKEN.
I also just read a theory that once the curse is broken… everyone remembers they have freedom… return to FTL, venture into the real world, leave SB …. go to the other realms if they know how to get there….