I'm not believing anything until cameras start rolling. I read/heard something that said "Bravo is scrambling and only Lisa is secure, but they may pull a Dallas with SLC" - despite Andy saying just last week that they have amazing casting for season 4.
With only 4 returning Housewives, Bravo would be dumb to not at least keep the Angies in the wings in case things with the potential newbies don't work out. These days so many things happen to change initial plans - a newbie might be boring and get axed (see Janell Stephens for RHOA season 15), might quit or be axed mid-way due to unforeseen circumstances (Nicole James RHOC 16), or film full-time and be demoted due to legal/contractual issues (Sutton Stracke, LaToya Ali.)