I think you're not talking about GitHub. Because I see A company which started from zero, revolutionized SCS, socialized coding. Makes a lot of cash, not from advertisement, but from an actual useful product. A Product that people love to use. I think A16Z is a very clever firm that invested in a very solid product.

GitHub has 102 employees. Which means they're already paying around $10M wage in a year and they're profitable. I bet they're at least making $20M per year right now. They're going after the enterprise market which would make them much much more cash.

Do the math. Is it really hard to pay that money back in a company like this ? Is AirBnB, Dropbox, Evernote in trouble ?

Github is not troubled.