Although it would hurt like hell, if Sanchez is desperate to leave then get rid of him—even to Chelsea.
The most outrageous outgoing deals don't matter, all that matters is a relentlessly positive response from the club. Sanchez leaves? Then sign two bigger players than him.
That's where we fucked up on the RVP scenario and in many other situations, not in letting him leave.
It would be a mistake to tie Sanchez down to his contract. Let him go, get in a new manager, Sanchez's absence takes the pressure off the new guy a bit.