Source: TransfermarktMessi's statement regarding this transfer is that he doesn't want to be in the same situation when he was at Barcelona two years ago and now he wants to prioritize himself and his family, therefore he has discouraged his intention to return to Barcelona or even go to the Saudi league.
I believe Messi made a very wise decision his future and career and inuding that of his family. No player has an everlasting affirmity with any club and it was just a contract between Messi and Barcelona.
There's no doubt that Barcelona has done alot for Messi and his family and I'm return Messi has done alot for Barcelona in terms of commitment and hard work. These two parties may never meet again in the football world. I am happy for Messi that he didn't make same mistake that Ronaldo made with Manchester United.
Yes, no matter how hard Barcelona wants to return Lionel Messi to Camp Nou, if the player doesn't want to return, then that will never happen. He is indeed the best player status Barcelona has ever had and he even became a legend there, but that doesn't mean Barcelona can arrange Messi where he will go. Now that he has decided to go to Miami to continue his football career there, I am not sure whether he will decide to retire there or not.
A player will not think about himself when he decides to join a club, considerations such as family will also affect where he will go.