As a longtime fan of Frank Herbert's 'Dune' series, I can confidently say that the books do not have multiple endings in the traditional sense, like a choose-your-own-adventure story. However, the series does evolve in complex and unexpected ways, especially as it progresses beyond the original novel. The first book, 'Dune,' has a definitive ending for Paul Atreides' arc, but the sequels—'Dune Messiah,' 'Children of Dune,' and beyond—expand the universe dramatically.
Herbert's writing is layered with philosophical and political themes, and each book builds upon the last, offering new perspectives and outcomes for the characters. For example, 'God Emperor of Dune' takes a massive leap forward in time, drastically altering the trajectory of the story. While there aren't alternate endings, the series' depth and the way Herbert explores different facets of power, destiny, and humanity make it feel like a constantly shifting narrative. The later books, especially those written by Brian Herbert and Kevin J. Anderson, add even more layers, though purists debate their canonicity.