What if they do? What if they don't even anticipate the direction they're "supposed" to go? What if they try rigorously to follow the "plot" and all the bright glowing question marks they find, but they break something? What if one of PCs absolutely won't do something the PCs are presumed to do, or absolutely will do something the modules assumes they won't? What if they roll badly? What if they don't know the name of the module, and they think they are supposed to go to Thay?
Like, I don't know what your social contract is, but I've always assumed you don't generally do stupid stuff. Randomly going to Thay can be stupid. But so can sticking to a module that doesn't account for reasonable, and more to the point, interesting behavior. And if the players don't have the freedom to do what they think they should do, they're not really playing an RPG. And that, to me, is a very serious breach of the social contract. If the module, or properly the DM, insists the players do something that is just unappealing or stupid, just to move things along, that is just an abject failure of design.
If doing A instead of B "ruins the DM's work," I question how much work the DM really did.