He put 12 gallons of oil in it?

Someone can get away with a little over filling the oil, but that is A LOT. The results can be catastrophic in a number of ways.

Sorry to read about this and hopefully the outcome is not too costly or time consuming based on the availability of parts or a replacement vehicle.

Piggybacking on what David wrote, below is a link the the 6.7L PSD sub-forum where you may have more informative responses.

Link: https://www.ford-trucks.com/forums/forum205/

 

What would/could be the results of such an error? Shouldn't the excess be blown out the blowby tube? Presuming it has one, it has to have a breather of some sort.

 

I'm a little incredulous that 12 gallons of oil could even be poured into the fill neck without it overflowing out of somewhere.

 

Basically, the answer is yes. If enough of that oil gets sucked down the intake, then there's the possibility of hydro lock and engine runaway. After making sure the oil level is proper, I would remove the intercooler and drain it for an hour. Anything else will just have to be driven out, along with making a very alarming amount of smoke out of the exhaust. Like insect fogging on steroids, LOL.