Why won't this roblox script save?

I made this script to load and save data. How can I make it save if a player joins and quits very quickly? It will discard the data if I leave quickly? I tried several things, but none of them seem to work. It would suck if someone quickly joined, received a lot of loot, and quit and it all got trashed. Is there any way to tell the server to save it all before shutting down? It seems that SetAsync() is doing nothing!

local Database = game:GetService("DataStoreService"):GetDataStore("MAIN")
local RStorage = game:GetService("ReplicatedStorage")
local PlayerIndex = {}
local CanSaveData = true
local BFunctionF = Instance.new("Folder", RStorage)
function SaveData(Player)
    local SCS, Result = pcall(function()
        Database:SetAsync("USER"..Player.UserId, PlayerIndex[Player])
        while Database:GetAsync("USER"..Player.UserId) ~= PlayerIndex[Player] do
            Database:SetAsync("USER"..Player.UserId, PlayerIndex[Player])
            warn("Stupid")
        end
        CanSaveData = true
    end)
    if not SCS then
        warn(Result)
    end
end
BFunctionF.Name  = "DataManagerBindableFunctions"
game.Players.PlayerAdded:Connect(function(Player)
    local ChangeData = Instance.new("BindableFunction", BFunctionF)
    ChangeData.Name = Player.UserId

    local Stats = Instance.new("BoolValue", Player)
    Stats.Name = "leaderstats"  

    local LevelStat = Instance.new("IntValue", Stats)
    LevelStat.Name = "Level"

    local CrystalStat = Instance.new("IntValue", Stats)
    CrystalStat.Name = "Crystals"

    local MoneyStat = Instance.new("IntValue", Stats)
    MoneyStat.Name = "Money"

    local SCS, Data = pcall(function()
        local RawData = Database:GetAsync("USER"..Player.UserId) or {}
        local NewData = {
            ['Level'] = RawData['Level'] or 0,
            ['LvlXP'] = RawData['LvlXP'] or 0,
            ['Money'] = RawData['Money'] or 0,
            ['Crystal'] = RawData['Crystal'] or 0,
            ['Bonker'] = RawData['Bonker'] or 0,
            ['Sword'] = RawData['Sword'] or 0,
            ['Hammer'] = RawData['Hammer'] or 0,
            ['Knife'] = RawData['Knife'] or 0,
            ['Brick'] = RawData['Brick'] or 0}
        return NewData
    end)

    if SCS and Data then
        PlayerIndex[Player] = Data
    end

    MoneyStat.Value = Data.Money
    LevelStat.Value = Data.Level
    CrystalStat.Value = Data.Crystal

    ChangeData.OnInvoke = function(Type, Amount)
        print(Player, Type, Data[Type])
        if Data[Type] == nil then
            warn("Fake Playerdata Type")
        else
            local NV = Data[Type]+Amount
            if Type == "Crystal" then
                CrystalStat.Value = NV
            elseif Type == "Money" then
                MoneyStat.Value = NV
            elseif Type == "Level" then
                LevelStat.Value = NV
            end
            Data[Type] = NV
        end
        print(Data[Type])
        return Data[Type]   
    end
end)

game.Players.PlayerRemoving:Connect(function(Player)
    if CanSaveData then
        CanSaveData = false
        SaveData(Player)
    end
end)
game:BindToClose(function()
    for O, Player in pairs(game.Players:GetPlayers()) do
        if CanSaveData then
            CanSaveData = false
            SaveData(Player)
        end
    end
end)

How can I fix this?