I don't think it's truly never - ending. While her story was very complex and full of twists and turns, like her conquests in Slaver's Bay and her march towards Westeros. Eventually, all stories in 'Game of Thrones' have an end point, and hers ended with her downfall in King's Landing, which was a shock to many fans.
Well, one way is to have multiple branching storylines that can loop back or lead to new possibilities. Also, incorporate player choices that have significant and long-lasting impacts on the narrative.
As far as I know, there may not be a 'Never Ending Story 3' officially released. But the film industry is always evolving, and new projects can come up unexpectedly.
Her constant growth and new challenges. Every time she overcame one hurdle, like taking over a city in Essos, a new one popped up. And her dragons added an element of unpredictability. With them, she could always strive for more power or face new threats.