They will NOT die at 100,000 miles.
the G8 is a simple basic car designed to get good mileage get you around, there's no flash to it, no pizazz.. it's designed to go against the pscion tC.
I wouldn't buy one only because Pontiac will soon have limited models, the car will have parts available for at least 15 years, but there won't be much in the way of support, in terms of newer ones.