In 301 BC, during the battle of Ipsus, Antiochus was commanding the left flank of the allies. His flank was soon routed and pursued by Demetrius cavalry, but Antiochus survived, while Seleucus cut off Demetrius from the rest of his army using elephants, allowing the main Antigonid army to be outflanked and defeated. What if Antiochus died at Ipsus, during the pursuit by Demetrius? How does any ATL successor to Seleucus I fare at keeping the empire together?