What would happen if somehow, the Seleucids are restricted to only the territory that the Parthians ruled. An obvious scenario for this would be the Romans kicking them out, but what about the Ptolemies doing that or them never even gaining Syria in the first place? Bonus points if the Seleucids last past the date of the fall of the Parthians and extra bonus points if the Muslims destroy a Seleucid/Hellenistic kingdom in Persia, providing of cause Islam still exists. Maybe Seleucid Arabia? What if?