If "letting the terrorists win" means getting out of mideast hellholes, ceasing to assassinate civilians with drones, and stopping the continual interference in various places they consider holy, then yes, I'm absolutely suggesting that.
We need to let go of the idea that it's us or them, and that either we win and they lose, or they win and we lose.
Wouldn't an outcome analogous to the modern-day UK and Ireland be great? People getting along well, no violence, reasonably stable governments? I don't see why you paint this as a bad outcome.