My function get called the first time, but never after, is there a way to fix this?

The monsterExp function only gets called once. I assume it is because the monster variable gets emptied when to gameObject gets destroyed. Is there any way to work around it. Also, another question, can you make labels update "live" and not after character reset?

monster1 = game.Lighting.Zombies
monster1.Parent = game.Workspace

exp = 0
level = 1
expreq = level*25 + 100
gold = 100
game.StarterGui.StatsGui.Level.Text ="Level: "..level
game.StarterGui.StatsGui.Exp.Text = "Exp: "..exp.."/"..expreq
game.StarterGui.StatsGui.Gold.Text = "Gold: "..gold


monster = workspace.Zombies.Zombie.Zombie
function monsterExp()
	print('hej')
	if monster.Health <= 0 then
		exp = exp + 25
		print(exp)
		game.StarterGui.StatsGui.Exp.Text = "Exp: "..exp.."/"..expreq
		print(game.StarterGui.StatsGui.Exp.Text)
	end
end

monster.HealthChanged:connect(monsterExp)

Replace your current function and connection with this:

monster = workspace.Zombies.Zombie.Zombie

function monsterExp()
    print('hej')
    --if monster.Health >= 0 then -- don't need this anymore
        exp = exp + 25
        print(exp)
        game.StarterGui.StatsGui.Exp.Text = "Exp: "..exp.."/"..expreq
        print(game.StarterGui.StatsGui.Exp.Text)
    --end
end

monster.Died:connect(monsterExp)

    monster1 = game.Lighting.Zombies -- change to ServerStorage
monster1.Parent = game.Workspace
 
exp = 0
level = 1
expreq = level*25 + 100
gold = 100
game.StarterGui.StatsGui.Level.Text ="Level: "..level
game.StarterGui.StatsGui.Exp.Text = "Exp: "..exp.."/"..expreq
game.StarterGui.StatsGui.Gold.Text = "Gold: "..gold
 
 
monster = workspace.Zombies.Zombie.Zombie -- what the f***?
function monsterExp()
   print('hej')
   if monster:FindFirstChild("Humanoid") == nil then Instance.new("Humanoid",monster) end
        exp = exp + 25
        print(exp)
        game.StarterGui.StatsGui.Exp.Text = "Exp: "..exp.."/"..expreq
        print(game.StarterGui.StatsGui.Exp.Text)
end

    if monster.Humanoid.Died:Wait() then 
monster.Humanoid.Died:Connect(monsterExp)
end