Watch in the replay of my Zombies match how I landed hard after the Mimic threw me from the rooftop and I forgot to hit my chute after my teammate just warned me about it and I insta-died. This can also happen when you try to takeoff with the Scorcher and hit a glitch. It makes you land hard and you experience what is known as perma-death. When you died, hopefully you drank a Tombstone like I did. I have lost my Relics over and over again and finally just started using a Tombstone before every match while I carry in my gold items that have already been upgraded from the purple items that I need to unlock the Season 3 Reloaded rift.
–Update: The Tombstone method that I described below didn't work and my Tombstone didn't spawn after Perma-Death.
–What to do: If you land hard, can't plead out, and see a red skull by your name, then you can't be revived. If you drank a Tombstone before you perma-died, then you should have all the things in that were in your rucksack in your Tombstone when you join the next match. I suggest waiting for your teammates to finish their game if you went in with a squad so that you don't accidentally lose your Tombstone, just stay with your squad in the game if you guys are already in a MWIII party. The next game you join, you will see a Tombstone logo on the map, drive, fly with a scorcher or jump pad to parachute to it, and then breakdown your Tombstone by emptying it, and you should also receive the money you have accrued when you access your Tombstone.