날아가다 is something flying off, and with a condition it stresses how little it would take: [바람 불면 날아갈 듯 얇디얇은 포토월], 한번 툭 치면 날아가고 그러더라고요, 아니 한번 치면 날아갈 것 같은. It also covers a substance boiling off (100도 이상 튀겨버리면 날아가는 거죠) and, in one line, a price shooting up the moment you sell: 팔면 날아가요!. So the same verb can mean disappearing or soaring, depending on what is doing the flying.