Congrats for taking action!
As others have said, do follow through - keep up the moving out motions, don't talk about the new roomie, do get the new roomie on the lease. I definitely like the "my other friend saved me by taking over the lease" idea about explaining the new roomie to friends afterward.
That said, your main friend group sounds like what my dad would have called a circle of patsies. If New Roomie is not as good as you hope, learn from your mistakes and upgrade your roommate search and management procedures. I have over a decade of happy roommate experience, but did read a book on "how to interview" early on, and did use explicit agreements.
PS. I think your new roomie will probably be great, but it's always smart to make sure all the bases are covered.