How to remove a plugin gui from CoreGui?

I'm making a plugin that involves the plugin's control GUI to be added to CoreGui. I want it to work so that if you click the plugins toolbar button, the GUI shows, and if you click it agian, the GUI goes away, and so on (click it again and it shows again). The only problem is I can't figure out how to remove the GUI from CoreGui without destorying it altogether, making it unable to show agian. Here's my current code:

--PLUGIN VARIABLES--
local toolbar = plugin:CreateToolbar("Animation Cam")
local coregui = game:GetService("CoreGui")
local version = script.Parent.Version
local gui = script.Parent.PluginGui
local open = false
--PLUGIN SETUP--
local pluginButton = toolbar:CreateButton("Rig Viewpoint","h","")

--local focusButton = toolbar:CreateButton("Focus","Label","")
--local fixButton = toolbar:CreateButton("Fix","Label","")

pluginButton.Click:connect(function()
    if open == false then
        gui.Parent = coregui
        open = true
    elseif open == true then
        gui:Destroy()
        open = false
    end
end)

I should note that I have also tried to make a close button as part of the GUI itself to close it, but for some reason the button didn't work at all. Here was it's code (inside the GUI itself):

local title = script.Parent.title
local close = script.Parent.Close -- close button
local coregui = game:GetService("CoreGui")

title.Text = "-Rig Viewpoints (V"..script.Parent.Parent.Parent.Version.Value..")-"

local rigs = game.Workspace:FindFirstChild("Rigs")
if not rigs then
    local text = Instance.new("TextLabel")
    text.Size = UDim2.new(1,0,0.15,0)
    text.Position = UDim2.new(0,0,0.4,0)
    text.Text = "ERROR: No Rigs folder detected"
    text.Name = "ERROR"
    text.Parent = script.Parent
end

local viewpoints = game.Workspace:FindFirstChild("Viewpoints")

if not viewpoints then
    local text = Instance.new("TextLabel")
    text.Size = UDim2.new(1,0,0.15,0)
    text.Position = UDim2.new(0,0,0.4,0)
    text.Text = "ERROR: No Viewpoints folder detected"
    text.Name = "ERROR"
    text.Parent = script.Parent
end

close.MouseButton1Click:connect(function()
    script.Parent.Parent:Destroy()
end)

I couldn't get the click function to work at all, even trying to simply make it print "!" to the output wouldn't work, so I'm not sure if there's something special you have to do when coding inside a GUI that's inside CoreGui.

All help is appreciated!