Another idea to add to this: imagine you can start underground... ( and you can add grow lights ) .... instead of an "all underground map" simply....fill *everything* above ground level with water! sure, you can dig horizontally relatively safely....maybe? and you can dig up.... but hit that ocean above you and you die and flood the caves you live in, or maybe you don't Might also be interesting when you're digging a new "grow room" and hit sand.
Anyway: If you respawn above ground: you drown
but still no zeds spawning underground..... so maybe something you'd have to mod a server manager to do...ugh