They've had opportunities to take CBs higher, they also took their safeties before they took corners even though they needed both.
And yes, Sherman is one of the top CBs in the league. But I do think he's very much a system player, and not nearly as close to as valuable to the defense as ET. If they see Sherman as expendable, because they don't believe in spending money on corners, or there's someone cheaper out there that can step in and so similar things, or if the league adapts somehow and they want to alter the system, or if Sherman can't find enough people to feel disrespected by to keep that chip on his shoulder and his production falls, I can absolutely see us letting him walk.
They've had several opportunities to draft a QB higher than Russell.... Does that mean they don't covet Russell?? Argument holds no merit.