Why does this script only run once after the player dies?

I am not sure if this works can you try it?

local player = game.Players.LocalPlayer

game.Players.PlayerAdded:Connect(function(player)
    player.CharacterAdded:connect(function(Char)
        local leaderstats = Instance.new("Folder", player)
        leaderstats.Name = "leaderstats"

        local level = Instance.new("IntValue", leaderstats)
        level.Name = "Level"
        level.Value = 1

        local exp = Instance.new("IntValue", leaderstats)
        exp.Name = "Current"
        exp.Value = 0

        local maxExp = Instance.new("IntValue", leaderstats)
        maxExp.Name = "Max"
        maxExp.Value = 100

        local truevalue = Instance.new("BoolValue", leaderstats)
        truevalue.Name = "TrueValue"
        truevalue.Value = false

        exp.Changed:Connect(function(val)
            if exp.Value >= maxExp.Value then
                Char.Humanoid.Health = 0
                player.Level.Current.Value = 0
            end
        end)
    end)
end)

So the reason it doesn't work is because the player.CharacterAdded is under the Players.PlayerAdded, and a player only gets added once, which means Players.PlayerAdded won't fire again and because player.CharacterAdded only fires if Players.PlayerAdded fires, the script won't run again after a player dies. To fix this, separate them, like this:

Put this in a server script:

game.Players.PlayerAdded:Connect(function(player)
    local level = Instance.new("IntValue", player)
    level.Name = "Level"
    level.Value = 1

    local exp = Instance.new("IntValue", level)
    exp.Name = "Current"
    exp.Value = 0

    local maxExp = Instance.new("IntValue", level)
    maxExp.Name = "Max"
    maxExp.Value = 100

    local truevalue = Instance.new("BoolValue", player)
    truevalue.Name = "TrueValue"
    truevalue.Value = false
end)

Put this in a localscript inside StarterPlayerScripts:

local player = game.Players.LocalPlayer
local maxExp = player:WaitForChild("leaderstats").Max
local exp = player:WaitForChild("leaderstats").Current
local level = player:WaitForChild("leaderstats").Level

player.CharacterAdded:Connect(function(Char)
    exp.Changed:Connect(function()
            if exp.Value >= maxExp.Value then
                    Char.Humanoid.Health = 0
                    player.Level.Current.Value = 0
             end
        end)
end)