Controversial post incoming:
Let's have a look at a hypothetical situation. Barcelona receive a record bid for Lionel Messi, a bid so high it'd be madness to turn down but also hard to accept because Messi is head and shoulders the best player in the world. All sentimentality aside, I believe it'd be beneficial for the club in the long run to accept the bid. Now, I know what I'm saying is sacrilege but hear me out. Lionel Messi is irreplaceable, that is an undisputed fact. This however, is a double-edged sword. Messi is so talented he brings Barcelona to a new level whenever he plays, but the negative is that when he is injured or suspended he does the opposite because of how irreplaceable he is! The problem with relying on such a unique piece to the puzzle, when the aforementioned piece is missing the whole puzzle falls apart. My proposal is that if in the situation Messi is sold then Barcelona would change from 'Messi and Friends' to simply 'Barcelona' again. It would create an atmosphere that would allow other players to seamlessly slot into other roles; which is currently impossible due to the uniqueness of Messi. Luis Suarez and Neymar while special players are far easier to 'replace' than Messi; nobody can fufill the duties and the role that Messi does. While Barcelona wouldn't be as fantastic as a team without Messi, they could be a more 'well rounded team' without the reliance of the mercurial magician.
Would I sell Messi if was on the board of Barcelona? No, I would not. However, there are benefits to a team that 'interchangeable' as opposed to a team with a 'marquee player'.