Not a chance.
The book is fiction. Historical fiction takes an imaginary story and surrounds it with historical facts or historical supposition. Despite my (marginal) interest in conspiracy theories, there’s not enough historical data to make the story of Mary’s involvement in the Knights Templar more than conjecture, and the idea that she and Jesus were married is pure fiction. There’s not a shred of evidence that Jesus was married…and that lack of evidence is NOT evidence that the Roman Catholic Church destroyed it all.
Another thing keeps me from buying into it all: superstition. If the book were true, and if Jesus’ descendants were alive today, what would it matter? Jesus came to earth to die on the cross. His children would simply be…children. They wouldn’t be the saviors of the world, would they? We only needed one savior…and if His kids were somehow more than human, why would they have allowed the world to become as it has on its own? Why wouldn’t they have shaped politics and religion so that the truth were known all along?
Dan Brown’s story makes for intriguing reading…but while stories of the Priory of Sion and the Knights Templar and cover-ups and alternate histories and the like are interesting, I find that they are always classified accurately at the bookstore: fiction.