Hey, its possible that some information can be recovered. But I wont guarantee all information will be in tact.
I had a External HDD which I loaded several hundred pictures into it. The wire got loose and the 500 GB disk was corrupted. Now, everytime I insert it in, the name which used to be Ryan (my real name) is now IMG@284.bin. I can open it, but anytime I click on ONE image file my computer gets a Kernel Panic and forces me to shut down. So, I think I get what you mean there, and the frustration of it all 😠
What the guy at the Genius Bar said is true; A hard drive that failed means it can no longer be used. Your files will be corrupted (like in my HDD case) and since yours is a MacBook Air, the Battery, Hard Drive, and RAM cannot be taken out. The only sad resort; get a new Mac. This time, get a MacBook, or a MacBook Pro (like me). Its faster, longer battery life and can be repaired when needed. 😉
I'm sorry for you, robbes. I really am. Do you have any important info or private things in that Air? They might be corrupted, or even gone. 😢
(Oh, and I don't actually know how the Genius Bar works or if they even lie to get your money. I live in Singapore, and there are no Official Apple Stores here, and I'm only 12)