FaceTime is fixed!
Update is out. iOS 12.1.4 fixes the bug as well as another security issue that Apple found while auditing the code for FaceTime. Group FaceTime has now been turned back on (for those on 12.1.4 or higher).
FaceTime Isn’t Broken
On Monday night (January 28), talk of a serious Group FaceTime bug hit the internet in a big way.