Originally posted by Fzanco:

Tombstone stays on map forever, tombstones will only generate though if you have something in your inventory. There's a few more details to know but I think this answers your main query for now

Well I have never experienced what you say in that once I loot my tombstone ( I'm buried there ) it disappears and is replaced with a skull and crossbones which stays on the map forever.
https://steamcommunity.com/sharedfiles/filedetails/?id=2517506938
Note no skull on mini map yet
https://steamcommunity.com/sharedfiles/filedetails/?id=2517506736
once I get my gear back
https://steamcommunity.com/sharedfiles/filedetails/?id=2517506348