WRONG. Very strong word.
If the airliner was at FL30 and the cabin depressurized, the passengers might die, the pilot would probably get his mask on and land the plane safely. So, a crash is not certain.
Anyone that could hit an airliner at 30,000 feet with a .50, again, deserves a MARKSMANSHIP AWARD.
Think about it a minute OK. There are pumps that pressurize the atmosphere inside the plane. They might work hard to over come the loss in pressure due to the hole, and might slowly lose pressure. Plenty of time for the pilot to get the airplane down to 10000 feet.