There are those here who say they don't give a ****, toss the thing around and have it in perfect condition, and others who say it's wrapped in plastic 24/7 who get scratches. So it's hard to say. As for the internals, the only moving part in the Late 2013's is the fan I believe, if you drop it, unless a wire or something is knocked loose (doubt it) then the damage will be cosmetic.. or the screen.
I bought a Speck SeeThru for my rMBP because not only do I have my laptop in transport all the time (laptop bag), but I'll be going to camp this summer to work, some extra protection is always good. I recommend this case if it's something you're looking at. They can be found for less than MSRP price on Amazon, just make sure you read the reviews.