I still think Messi is completely focused on Copa and will consider options once it ended. Ultimately he will stay, but negotiations won't make much progress during Copa.
If they lose the final to Brasil, he may strop and decide to retire [for a few months].
New best case scenario.
Brasil beat Argentina 5-0.
Messi retires.
January Messi decides to come out of retirement and sign for MLS team for 6 months.
Messi signs for Barcelona next Summer