But somehow he owes you not going to direct rival? Loyality is a funny thing, man. It works both ways.
The best move for you was to offload him last summer when he still had 2 years in contract. At this point the club really doesn't have much say in the matter, Cech will go where he wants. Holding club legend hostage in reserves to block a transfer would be PR nightmare of epic proportions.
Cech doesn't owe us anything either. He can head where he wants but as he is under contract with us, Chelsea still have a say over his final destination