The long timing chains used in these engines do wear, but at a much slower rate then in say a belt driven OHC system. The likeliness of the chain outright breaking is just about as good as the chain breaking on your standard pushrod V8, so almost no risk at all
If memory serves me correctly, the EcoBoost torture engine had adjusted itself up two teeth in the timing belt tensioner mechanism. It has something like 10. Like the others have posted, just should not be an issue over the life of the engine.