While the show has certainly not earned faith when it comes to explaining the fantastic, since that question will absolutely be brought up, perhaps we should wait before assuming we will hate the answer. My guess is it will either be something big picture like evil is necessary for balance and thus can’t ever be fully eradicated simply controlled and harnessed or it’ll he related to magic being different in the real world or something like that.
In season 4, there was a deleted scene of Rumple finding the dust left by Elsa’s urn and explaining to everyone that magic can never be destroyed, just change forms. The scene was cut so they later had Rumple give a truncated version of that speech to the Snow Queen when he used that dust to neutralize her. It’s why the idea of destroying the Dark One never made much sense to me. It seems like the magic would always exist, you could just maybe change it somehow. I wondered if the Evil Queen’s resurrection had something to do with that. Of course, it’s probably silly of me to think the show remembers a line of dialogue from season 4.
When I saw the Evil Queen crumbling to dust, then ‘returning’ to life I had two thoughts:
1) We saw Zelena surviving being killed by transforming before. She turned into a statue before Rumple stabbed her and then she somehow went in an energy stream to her magic locket before respawning.
I usually try not to think about it because I never liked her coming back to life like that. It felt like such a retcon because watching 4A, knowing Zelena is Marion just doesn’t seem right. She nearly died from the Snow Queen icing her heart – I can’t imagine Zelena not fighting back over that. Anyway, I digress. My point is they have faked us out with a transformation death like that before – it has precedence.
2) Two sides to the coin, two halves of the same soul. Regina and the Evil Queen aren’t two people, they are the same, magic has just split them into two bodies. Therefore, given that they are still connected (being the same person) I would think that you couldn’t kill one without killing both.
Regina crushed the Evil Queen’s heart, but that was using magic to destroy a magical construct. That wasn’t really a heart, because Regina’s heart is still in her chest, so crushing it isn’t going to do anything.The Evil Queen can’t be killed, not physically anyway, not unless Regina dies too because she is both.
I read a fanfic once, I forgot what it was so I can’t link it sorry but Belle accidentally released a genie who was under instructions to kill Regina – it was an unfilled wish. They got it ‘completed’ for him by saying that Regina wasn’t the Evil Queen any longer. That the Queen was dead and Regina herself had killed her by changing. I rather suspect that the show will wind up doing something similar, and the Evil Queen will be ‘killed’ by acceptance.