Nadia Bjorlin, who plays Chloe, was pregnant, so will be on the show for a while, then takes maternity leave. (in real life, that is when she had her baby, which was early May). She returned to the show when the leave was over.
And in reply to RS, guess there was a typo, as I understand Marci Miller will be playing Abby DiMera, and is supposed to be arriving back in Salem in November.
Most of that info is here on this board in the various spoiler threads in the Crystal Ball.
The actor playing Philip has been let go, and while the actors portraying Shawn D. & Belle, were also let go a few weeks ago, Brandon Beemer (Shawn) was brought back. So it would appear unless the show decides to being Martha Madison (Belle) back, she will be departing Salem first, a few weeks later it will be Philip. In the near future, both Summer and Fynn will also be leaving Salem.
And, by the way, Jen Lilley, who plays Theresa, and decided to leave the show, has stated that the return of Shane & Kim (Theresa's parents) have NOTHING to do with Theresa's departure.)