considering how difficult justine and caroline are, i have a feeling that they won't give you a chance to fight him because you'd lose. he is the master of the velvet room, you can't stop him.
also, p5r isn't necessarily a remake or whatever.
Persona 2 let you fight Igor's boss, though he barely uses any of his true power in the fight. Based on how that fight works though...Igor would probably be equally as bad if not worse because he wouldn't have to hold back as much.