Standard procedure is max FL100 or 10 000 ft.

But if you are flying over mountains (FL180 for the Alps highest safe flight level) you are fucked.

Well no, there are oxygen masks and the pilots will immediately put them on and then dive toward a safer altitude at a controlled but fast rate of descent (more eardrums bursts).

Airbus Procedure is basically “Pull everything on the MCP !”:

• masks on for both pilots,
• checks interphone com with your Captain/FO.
• On the MCP, autopilot set altitude to max FL100 or below (above if mountains), pull for open descent,
• pull for HDG and go off track (outside the airway to avoid collisions).
• Pull for max Speed or appropriate (not in managed mode anymore, this will change your rate of descent).
• Speedbrakes max.
• Transponder 7700
• Then you can call Mayday on radio.
• You also check that the masks had been automatically lowered in the cabin at that point.

And A320 should descent at around 7000ft per minute. Could be more or less, it’s the pilot choice and how much he is willing to stress an airframe that just had an explosive decompression.

Rapid decompressions are very rare events tho. Except maybe on 737 max.