Some uneducated players move markers out of the map instead of CTRL+SHIFT+right click. What if they are automatically destroyed when they leave the map or after several minutes?
Destroy markers when they leave the map
If the marker is still visible for you and confused you, then delete it yourself
Otherwise except when using space to tilt the camera a lot the markers shouldn't bother you at all once they were moved as far out as possible.
Personally I'm the type who deletes any markers after a short time periode cuz they're annoying, so far noone complained about it lol.
Required rating for participation in balance talks when?
I think automatically deleting them might not be a good idea, since people might actually put markers outside the map as notes or something.
So without a good reason to I wouldn't auto delete them.