First, sorry for your unfortunate accident. Nobody should ask why you dropped it... an accident is never intentional hence the name ACCIDENT!
Second, unfortunately Apple has a reputation on the forums of voiding almost any warranty for any reason like a bump or drop. It seems they can void the whole system if there is visible damage from a drop.
I hope that if you have any problems with it, that Apple will do the right thing and cover it under warranty. If you haven't bought AppleCare, I would avoid that until you get clarification from Apple, as it could be a waste of your money. I always recommend people use the standard first year warranty for the first eleven months, and then buy AppleCare just before the full year is up. Then if there has been a theft or a drop, you can avoid buying the AppleCare and save your money.
Some people have reported that after a drop if you pay Apple to fix it all, Apple will restore the warranty. But that could be extremely expensive.
Lastly, I have found MBA lids and cases on eBay for $35 to $50. If you have the experience, you could replace the case by yourself and then make the MBA like new.
Good luck.