I would try to flesh out the mythology of the realm and the magical lore. I would have a massive threat to the United Realms be Carabosse (who wasn't invited to the christening of Baby Hope). Carabosse was one of the three Ancient Fairies (the other two being the Enchantress and the Blue Fairy) before being banished for practising Dark magic and creating the Sleeping Curse.
Carabosse curses the entire UR (not like the Dark Curse but instead poisoning the entire realm so that it slowly dies) and kidnaps Hope. The heroes are now split into three groups:
1. (Led by Emma) those going to find Hope.
2. (Led by Regina) those trying to stop the flow of Carabosse's spell in the UR.
3. (Led by Henry) those trying to find a cure for the curse.
As Rumplestiltskin and Belle are dead there is no chance of them being resurrected.
New Characters:
Carabosse: main villain. A powerful sorceress with a wicked temper, Carabosse is one of three fairy sisters known as the Ancient Fairies who was banished because of her creation of the Sleeping Curse (which back then had no cure). She has quietly stayed out of the events of previous seasons and many thought she was dead. She desires revenge against her sister the Blue Fairy for taking away her daughter (Maleficent) and now curses as many babies as she can in revenge. She is young and beautiful.
Rhoswyn: also known as the Enchantress. Rhoswyn is the oldest of the three Ancient Fairies and appears as an old woman to fool people (though her true guise is a lovely maiden). Rhoswyn was brought to the edge of the UR by Regina's new spell and is sought out by Hnery to help with a cure for Carabosse's curse. I want to establish her as the grandmother of a pre-existing character but, since Belle is dead, I am struggling with ideas ... help! Also, Rhoswyn is known as the Godmother of the Rose because she once turned her godson into a vicious beast and tied his life force to an enchanted rose because he tried to destroy a village she was patron to.
NOTE: I want to hear feedback and am open to suggestions so please reply.