Scott,

Yes the bentonite will rehydrate but it may take years to really dry out depending on its thickness. As it drys, a crust will develop and the bentonite will form large prizms with wide cracks. You might want to sheepsfoot or disk it prior to rehydrating (if you can get on it) just to aid in redeveloping an even thickness especially as you said it is the seal for sandy soils.

As George said, it is only a type of clay which is highly expanding (and contracting) depending on moisture content. Ideally, if you bury it before it hydrates the added pressure makes it even tighter.