I said "can't miss" sometimes miss too, but it is at least a lot less likely than getting 3 prospects who are in a teams 4-10. Look at the group that has come up this year alone (Bryants, Correas, Pedersons of the world) and helped their clubs, if you don't get a guy with that level talent don't trade him. period.
Depreciating in the sense that we are all depreciating, sure. Depreciating compared to what else is out there, no. 3 more years of control at a reasonable price. He'll be just as valuable in the offseason or at next years deadline. Get a top talent prospect or keep him.
What if an offer with a Bryant/Correa/Pederson never arrives?