Any brick that doesn't have a brick underneath each unit of it should fakekill when touched from above (do this by looping its downbricks and checking to see if the total amount of horizontal area is greater or equal to that brick's total area).
The solution to stopping that from happening is simple; tunnel ceilings that people will be walking on the top of just have to be two bricks thick to stop them from breaking when walked on.
It would also be nice to see some kind of proper support system (for instance you can have two units of bricks beside the top of another, like how pillars work in the Sims, without them collapsing) but that might be a bit much.