Rumple isn’t impish green in appearance in SB, so maybe he’s not immortal here either? It’s never been made clear exactly why but chalk it up to hand-wavy, rule-bendy obfuscation I suppose.
Well Hook did stab him in the heart in 404 (while they were sitting in the car) and nothing came of it. So I suspect he’s immortal until his heart is “gone.” Then he’s rendered human again.
I’m hopeful that they won’t kill off Rumple, if only because at 4 seasons in they’re not likely to gain any new viewers so should be concentrating on maintaining the viewers and fanbase they have. Killing off Rumple would lose them half their audience.
And I’ve stated this many times: it doesn’t matter. I think ABC and A and E know that S5 is the last. It doesn’t matter if the ratings bottom out for S5 because it’s the last and they are going to get a 22 (we think, it’s the more likely of the two scenarios, the other being an 11 or 12 episode season) to play it out however they want. ABC also know that while Rumple is popular, Regina and Hook have extraordinarily vocal fans that probably, at this point, out number Rumple viewers.
I understand the inclination to say that they can’t kill Rumple because it would “kill the show” but ratings wise, story wise (a giant good vs evil season in which we learn a startlingly amount about the book, the Author, and have a mild philosophical debate about the nature of good vs evil all scream “we’re coming to a close), I think you’re missing the point: the show is dying. It’s dying a natural TV death that happens to all TV shows eventually, especially one stepped in its own mythos as heavily as ONCE is (those shows cannot sustain themselves like their episodic counterparts do).