With that low mileage and so much engine damage, I would have demanded a new engine. Even though your engine failed due to quality control at the factory, I would have more faith in a factory replacement engine than one "assembled" in a dealer workshop.
If you have anymore trouble with the engine, I suggest you demand a replacement.
Looks like it cost MB more to fix your engine than it costs some manufacturers to build an entire car. I'm glad you didn't have to pay for the repair.
P E H