Kind of a weird one. Personally, I have to imagine Barca will be in a better position in 2 year's time if they sold him at a stupid, stupid price and then spent the proceeds on 5 or 6 younger players to improve the squad. For those 2 years though, Messi obviously offers more.
Find it surprising that a player that has been there his whole adult life isn't a bit more loyal and pragmatic. He's made legacy money already, and it's not like sponsors aren't going to continue paying him for the rest of his life, not to mention investment returns and other ventures he could get into as a young man with huge capital.
He seems to be putting his 'beloved' club at real risk by asking so much, not to mention that presumably he'd also have a better time of it for his remaining years if he freed up some funds to buy better teammates.