The ai ERE usually loses to the Seljuks in thier opening war. If that happens then the Fatimids usually eat Greece within the next 5 years. Then the Seljuks mop up. In my current game, the ERE lost the first big battle but reduced the Seljuks army to around 3k troops which I was able to defeat with my levies and force a stalemate. Then the Fatimids got destroyed when invading Greece. So, the fate of the ERE is usually decided in the first 8 to 13 months of gametime. It all depends on the outcome of the first big battle.