[llama]

There are many ways in which you can do something like this, one example is:

pawn Code:

public OnPlayerUpdate(playerid)
{
  new Float:x, Float:y, Float:z;
  GetPlayerPos(playerid, x, y, z);
  
  if(z < 70)
  {
    SetPlayerHealth(playerid, 0);
  }
  return 1;
}

I'm sure there is a better way to do this, but this is one simple solution.