P!nk & Shakira on a WW scale. IDK about Gaga.
Rihanna probably couldn't. Her career is very dependent on what's hot now... She was struggling when she put out music that was even a little left of center (Rated R) just imagine what would happen if she didn't put out music at all.
Katy couldn't, she needs to keep up the momentum. K$ is already losing favour while in the limelight so I mean...
Rihanna more than deserves a break, and I think she could take a short one (2 years max) and be fine.
Lady Gaga could take a break and survive.
P!nk could take a break and survive, cause I feel like she doesn't really rely on a die-hard fanbase to be successful. Everyone just sort of likes Pink and will embrace her with at least moderate enthusiasm.
Shakira can take a break and maintain her global relevance, but I feel like she loses steam during breaks in the United States and there's always a question of whether or not she'll be able to win back American audience. Sometimes she does, sometimes she doesn't.