Alot of discussion has involved Alexander dying later then OTL, or at least some time during the Persian war. I don't think i've seen a discussion about him dying before being on the throne. Lets say he dies a few months before Philip does, and Philip is assassinated according to schedule (ignoring the possibility that Alexander was involved in the assassination).
So does Alexanders brother Philip take the throne? Or will his mental infirmities limit his chances like they did in OTL? And what is Macedonias battle hardened and effective army used for?