This is likely to differ significantly from a scenario where he dies, as the legitimate Great King is still alive, however, he has suffered an even greater humiliation than simply fleeing from the battlefield, but being captured. The Achaemenids have suffered a huge defeat, but the empire hasn't been truly broken to the same extent as had happened at Gaugamela, with a decent core in Babylonia and Persia still intact, and crucial time to raise another army while Alexander was defeating local resistance in the Levant. Does Oxyathres, his brother, attempt to rescue Darius, or does he abandon his brother and attempt to get proclaimed King of Kings? Does Alexander ransom him back for an ungodly sum, execute him, or keep him in captivity, pressuring him to adopt him as "heir"? Would Bessus start his rebellion earlier? Would Darius have a son, and what would be the impact?