Spot on, no guarantees he'd have developed as he has if he'd stayed here, in fact had he stayed it's doubtful he'd have gotten the mins needed to develop into the player he has. Dropping down the Championship permanently gave his career the kick start it needed. He'd never set the world on fire...
It depends on the terms of the buy back. There are two variations one allows the club to buy back at a set amount pre-agreed in the original sale. Obviously this works out great if the player really develops and you’ve agreed a low fee.
The other variant allows an agreement that you’ll match...