It looks like Aguero is really mad that Messi has officially left the club. He has come to Barcelona for Messi. And now it looks like Aguero wants to leave also.
Aguero is a professional football player, he won't leave Barcelona just because of Messi leaving. Also, I am sure the biggest reason why he came to Barcelona isn't about Messi. He must know Barcelona is a better place to get more titles and probably to have a new experience there.