Instead of Valka, it was Hiccup that was taken. I believe Cloudjumper intended to take Hiccup from the start. Join him on his dragon life. See how he meets Toothless in this scenario. See how Berk goes without their heir. What would happen? There is no... true answer. I am not the original creator, but I can give you my idea in this book. (Disclaimer: there is blood and violence in this story, read at own risk. You've been warned.)