When Cruella shared with the others how Ursula betrayed them, I'm worried that might go after her and hold her prisoner and possibily try to kill her! Do you think that could happen or will they just shrug it off and try to go on without her?
Personally, I don't see a need for her any more. So the other villains probably won't care too much. I think her leaving and getting her happy ending might inspire the remaining charachters to find their happy endings. Rumple's plan seems to include tearing everybody appart, so I would not be surprised if he anticipated some of the QoDs leaving.
It seems to me he only needed really needed all three of them to get into Storybrooke; once he was in he just needed someone to do his dirty work since he couldn't reveal himself. So he doesn't need all three of them anymore.
The only reason he would've revived Maleficent would be intimidation, because the Charmings are so afraid of her.