I would not worry about engine to be honest. It shares the engine with a Toyota Aygo, Citreon C1 and Peugeot 107, and so there is wide-ranging proof of the engine's durability. Over 100,000 miles, I would be more worried about the clutch. Whenever that goes, expect to pay a higher price to fix than in an Aygo as it is a lengthier job in the IQ so higher labour costs. Still though, I don't think you can go too wrong