Apart from the above how do you know he's "fainted"? Can you tell by glancing at him that he hasn't had a heart attack or a stroke, or is about to launch into a fit? That's a call beyond a Pilot's pay-grade. It's a Mayday and land for medical assistance asap imho.
For the mayday doubters, turn the scenario around and have the Capt incapacitated on finals - what call does the FO then make?
QED I think.