Assume the mutiny by Alexander's troops that forced him to turn back happened slightly later. Alexander waits it out a few days as per OTL, but here, in wonderfully perfect timing, Memnon arrives with his reinforcemence of 6,000 cavalry, 7,000 infantry, and 25,000 suits of armor (IOTL, Memnon unfortunately arrived shortly after Alexander caved). This might just be enough to persuade Alexander's men to press forward, and for the sake of the what if, assume that it is.
How does Alexander fare against the Nandas?