Here’s the thing, although Regina is a fan favorite, I don’t think she’s capable of carrying an entire show on her own.
Yeah, this has always been an ensemble show with a heavy focus on the connections between Emma, Snow, Regina, and Rumple. In order for Regina to carry on without the other three, you need to fill the void with characters who are equally compelling and have an equal meaty history with Regina. So the task before the writers would be astronomical. You need to create, flesh out, and develop at least 3 characters who have the same narrative weight to Regina that Emma, Snow, and Rumple already have but you need to do it in the span of one season instead of the former 6. Why one? Because the ratings are already so low and in order to push this “new” show, ABC and A and E have one shot (one season) to prove that a Regina focused show can survive and prosper just like OUAT did.