I also believe losing RC would end the show. I just can’t see it happening. Hook & Regina are definitely drawing audiences on their own, but without Rumple to balance their characters out…there’s no show.
And there is no show after S5, at least if we’re looking at ratings and predictions for forthcoming season ratings. S5 is most likely (I’d say about 85% sure here) the end. And even how they are presenting this arc’s story as the ultimate way to fill in a lot of the blanks and really tear apart what it means to be a hero or a villain. A lot of this story this season isn’t just “story of the arc” it’s “story of the show” and is being presented as a big wrap up, or at least the biggest heave ho before they do two smaller arcs in S5 and then bow out. And if A and E and ABC know that, then they don’t have to consider how the loss of RC affects the show and its ratings anymore. They can be a bit devil may care because it’s the end. They can bring in someone new for a short arc (Jafar seems like the biggest option and theory right now) and then end the show after that arc is done.