The modern engine runs pretty much forever, as long as you maintain it properly; that goes for the Mercedes engine as well as any other decent make. Of course some parts are semi-consumables, such as piston rings and cam belts etc. so you need to replace those, and eventually something more substantial is bound to fail but again most things can be replaced. (No different to your house - if a roof tile comes off, you replace it; if the walls need re-pointing, you get that done; but the house itself lasts more or less until you decide to pull it down and build a better one.) Something like 10-15 years and 200-300k miles isn't even much, I've had myself a car that I drove for 13 years and 220k miles, and it was still going strong.
That doesn't mean that you can drive a car forever, though. Usually the other things start to fall apart, such as the interior, electrics, air-con, etc., and eventually rust will also come through the body. And while those can also be repaired or replaced, at some point it all starts to get unfeasible - there's no point in doing $5k worth of work on a car whose market value by then is $500. So eventually you'll just scrap the car. And of course many cars get written off for various reasons - accidents, thefts, fire, etc. This is why the average age of all cars on the road are maybe 10 years - not because cars don't last more than that, but because the odds increase each year of something having happened that caused the car to be taken off the road.