I think Messi should go and try. He surely won't be the one to make them worse. His presence itself, at least I feel like that, gives Argentina a whole different power. He has no insane leadership qualities but people in Argentina worship him, and so do the other players. They have a special responsibility of not disappointing Messi, hence why most of them are completely different players for their nation and their clubs. That might change when Messi retires.
After all, Argentina has fair chances of going far into the World Cup. His teammates are good, he finally has a good coach and they go into the tournament with a lot of confidence.
But it's ok if Mara thinks he might get embarrassed, I understand that too. Anything can happen there and of course there are dangers. But I think, at the end when everything is over, all Argentinians will forgive Messi in that case. Nobody will forget 2022. There is nothing to lose for him really.