The Engine is part of the PowerTrain warranty from Mopar, GM, Hyundai, Toyota, Honda, Kia, Suzuki, Jaguar, etc.
What happened from my understanding is that his car has Dexcool, and the person who replaced the water pump added Ethylene Glycol (the green) which is not compatible with Dexcool. When you mix Dexcool with Ethylene Glycol, they form a gel-like substance that stops coolant flow and causes the engine to overheat due to non flowing coolant.
It will gum up everywhere. When you shut it down due to it over heating, the substances are usually mixed, and it gels up into a hard jello like substance everywhere there is coolant. Everywhere from your Radiator to heater core, and of course, the engine block.
If a shop replaced your water pump, they should be legally liable to fix the problem since they are the cause of it. Dextron has been used for many many years now, and any reputable shop should be aware of it. There is a chance that the engine could be saved. (well, not the radiator or heater core) using a high pressure system to try to flush the engine block. This has a high rate of success once the engine is removed from the vehicle.
as far as the dealer goes, the engine warranty was voided by the use of a non-approved coolant. it would be the same if you put diesel gas in your tank. Water pumps, brakes, axles, and most "wear" parts are not included in the drivetrain warranty of most places. However, if the vehicle is under a factory warranty sometimes its worth still going to the dealer to have repairs done (and none of this would have happened, and they may have possibly performed any recall work that you were unaware of)