How do I get the value to change when the NPC dies so it respawns?

This script spawns a random zombie from a folder on to a random block. But doen't respawn them.

I can't make it so that when of the created zombies dies it makes the number value go down, which in turn will spawn a replacement zombie. .

local NPCS = game.ReplicatedStorage.Enemies:GetChildren()
local number = 0
local max = 6

if number <= max then
    canspawn = true
    print("can spawn")
end 


while  canspawn do
    local ChosenNPC = NPCS[math.random(1, #NPCS)]
    local ChosenSpawn = math.random(1, 6)
    print(ChosenNPC)
    print(ChosenSpawn)
    wait(4)

    if ChosenNPC then
        clone = ChosenNPC:Clone()
        clone.HumanoidRootPart.Position = workspace.EnemySpawns:FindFirstChild("Spawn"..ChosenSpawn).Position
        clone.Parent = workspace.EnemySpawns.Spawned
        clone:MakeJoints()

        number = number + 1 
        print(number)
        if   clone.Humanoid.Health <= 0   then
            number = number -1
            print(number)
        end 

        if number >= max then
            canspawn = false
            print("Stoping spawning")
        end 


    end

end