Great mod, I love it - except when it can't find a spot to drop the tomb-stone, which I believe is the only case it disappears? Have you considered dropping a console note when that does not happen? It's been driving me nuts when I spend a lot of time looking for it (finally wrote a script). Thanks!

I have been thinking of a way to make the Tomb-Stones appear on the map ie like a train station, but am yet to find how the train stations do this :(
any hints would be helpful :)

Anyway on line 3 of the control.lua try changing the 16 to 0
local pos = game.surfaces[player.surface.name].find_non_colliding_position("tomb-stone", player.position, 0, 1)

see if that fixes the Tomb Stones not showing up problem.

Train Stops are hard coded to show on map.
If you want the tombstones to show on the map, create an invisible, indestructible train stop without collision, bounding box and set its backer_name = "tombstone "..player.name.
Orbital Ion Cannon and Smart display for example use that method.