In 333 BC, Alexander the Great battled the Achaemenid King of Kings Darius III at the battle of Issus. The battle initally went relatively poorly for the Macedonians, with both the left flank and the center pushed back, but the Hypastpists managed to break through the Kardakes infantry on the other side of the river and punched a hole in the Perisan line, with the Agrianians marching in support, causing Alexander and his companion cavalry to charge Darius III personally. Darius III, seeing his position compromised, fled the battlefield, despite the performance of his left flank. What if Darius III had chosen to remain with his isolated force of chariots and fight, being killed by Alexander's charge. This would throw the empire into chaos, with a civil war and rebellion in the empire quite likely. Would Alexander still fight an ATL Gaugamela? Would places like Egypt, Babylonia, or the Eastern Satrapies rebel themselves, or side with Alexander? Since obviously there wouldn't be the need to chase down Bessus, how would the conquest of the rest of the Achaemenid Empire go differently?