As the army withdrew, the affairs of Mexico came to a temporary close. As for the southern territories that were occupied, that would have to be slowly negotiated later.
Colonists from those years were not to be trifled with; what they swallowed, they seldom spat out. Even if the Vienna Government ordered them to abandon their claim, it's not guaranteed that they would comply, and with the current strength of the Mexican Government army, victory over these plantation owners was far from certain.
This was proven during the Civil War; when fighting for their own interests, plantation owners could always unleash greater potential.
No matter what intentions Maximilian I may have had, Franz promptly had him "escorted" back to Vienna. Just from the wording, one can tell that the process was certainly not harmonious.