There's a LAN Launcher you can download here that lets you play offline, just in case Plutonium does get the Cease & Desist letter.
Download Here: https://forum.plutonium.pw/topic/30141/offline-launcher-for-plutonium/24
It shows you how to set up the LAN Launcher.
** IMPORTANT! **
Set the "Plutonium folder" file destination to "C:/Users/Example/AppData/Local/Plutonium", then wherever you have your games installed at, just put the destination to the game in the empty bar.