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.
He decided like a good father and husband. Though the financial part of this proposed contract has not been revealed but I doubt if it will be bigger than the offer in Saudi Arabia. The decision he took might be after he has considered the social implication of his decision. The US is a freer society which means his wife, children, and family members will be able to adapt to the demands of society.
The US Major League might also offer more endorsement opportunities because the country has the biggest economy in the world. If I were Messi I would never return to Barcelona because I cannot guarantee that my performance can match my records. He might return and start having issues with the club and players due to poor performance or other issues which could taint his hard-earned reputation. It is better to remain a legend than to gamble with Barcelona.