Not if you literally just use a Firewall to prevent the Launcher from accessing the Internet. Because once you are logged in, you can play offline too, and there is as far as I know, no timeout for that Offline Login.
Also if it is for personal use it is legal on the DMCA part, since you literally dont distribute anything. That GitHub youtube-dl thing is NOT an actual DMCA takedown, GitHub just didnt have any infrastructure to block things and they had to act fast so they just used the DMCA as default, which kinda ended up misinforming people on what DMCA is and what it is not.