Datastore script saves one value but not the other?

The datastore can only save ONE value, so you'll need to get em in a table, and save the table, encoding it into json formatted strings(because datastores only save int's, number's and strings) just like that:

local httpservice = game:GetService("HttpService")
local data = {tix.Value,worlds.Value}
local encodeData = httpservice:JSONEncode(data)
datastore:SetAsync(key,encodeData)

and to decode

local Data = datastore:GetAsync(key)
local decodeData = httpservice:JSONDecode(Data)
tix.Value = decodeData[1]
worlds.Value = decodeData[2]

Now, your entire script emplementing that:

local httpservice = game:GetService("HttpService")
local DataStoreService = game:GetService("DataStoreService")

local myDataStore = DataStoreService:GetDataStore("myDataStore")

local playersLeft = 0

game.Players.PlayerAdded:Connect(function(player)

    playersLeft = playersLeft + 1

    local leaderstats = Instance.new("Folder")
    leaderstats.Name = "leaderstats"
    leaderstats.Parent = player

    local tix = Instance.new("IntValue")
    tix.Name = "Tix"
    tix.Value = 0
    tix.Parent = leaderstats

    local worlds = Instance.new("IntValue")
    worlds.Name = "Worlds"
    worlds.Value = 0
    worlds.Parent = leaderstats

    local Data
    local success, errormessage = pcall (function()
        Data = myDataStore:GetAsync(player.UserId)
    end)

    if success then
       	local decode = httpservice:JSONDecode(Data)
	tix.Value = decode[1]
	worlds.Valie = decode[2]
        print("Player data loaded successfuly!")
    else
        print("There was an error whilst getting your data!")
        warn(errormessage)
    end
end)

local bindableEvent = Instance.new("BindableEvent")

game.Players.PlayerRemoving:Connect(function(player)
    local data = {player.leaderstats.Tix.Value,player.leaderstats.Worlds.Value}
    local success, errormessage = pcall(function()
        myDataStore:SetAsync(player.UserId,data)
    end)

    if success then
        print("Player data successfuly saved!")
        playersLeft = playersLeft - 1
        bindableEvent:Fire()
    else
        print("There was an error when saving data!")
        warn(errormessage)
    end

end)

game:BindToClose(function()
    while playersLeft > 0 do
        bindableEvent.Event:Wait()
    end
end)

Hope I explained it well!