Yes, Mr. Box, the terrain will come on sprue... at least 5 sprue from what I have heard speculation on.
As for price, I was thinking 25% of the price of the box for the CSM. If it is the same price as Chalnath ($170 retail), then it would be $37 (25% of the standard discounted price of $145).
FYI, I'd be selling the terrain at 40% of the price of the box or $58.
In my mind, this is a true splitting of the box. I have no interest in making a profit off of the parts I do not want.