I have been trying to make a minecraft map in windows 10 edition but I can't get the setbock command to work if all of the mobs in the area have been killed.
A solution I found is that you can do a command
testfor this will test for entities:
This will test for all currently loaded zombies
/testfor @e[type=zombie,(r for PE, distance for PC)=20]
This will test for all zombies within a 20 block radius. Radius is building that many blocks off the sides and connecting them to a cube. Thus displaying radius. Than have a comparator coming out of the command block and redstone repeater followed by a solid block with a redstone torch