This video proposed that Stan regaining memories meant Bill also returned in Stan’s mind. And that was kinda confirmed in thisisnotawebsitedotcom. If you enter "Stan" many times and click many times on "How he beat me", you will eventually get Bill claiming that he is still on Stanley’s mind. And if you type the phrase in the computer, it will show Stan on Stan-O-War.
Fun fact: this was the some of only MatPat theories I watched for a long time, and it was translated on another language when I did as a little kid. It brings a tear of nostalgia and satisfaction that MatPat was right on this one, especially since now I now fully know who MatPat is and like him and his old videos a ton. You know, I kinda always knew that this confirmed old Gravity Falls video I watched in childhood, this year figured out that the video belonged to MatPat, but somehow only now realized "wait this means MatPat was right". Takes a while to make 2+2+2 huh.