Apparently Alexander Pereira, the Salzburger Festspiele and La Scala Milano have all come to an agreement that he will become the head of La Scala on October 1, 2014. See here. This means he will continue to manage in Salzburg through next year's festival. This change is a year earlier than planned and represents a large drop in salary for Pereira.
Reports seem to say that he left because of restrictions to his budget.