Honestly, I don't see Beyoncé going anywhere. She's well respected for her talents and apart of an iconic couple. She'll be around forever, tbh. I don't think over the next 10 years she'll be as in our face or consistent w/ musical releases, but she'll pop in every three or four years with an album while raising/having more kids. So, yeah.
Britney, is Britney. She's legendary, but I think her star has faded quite a bit since her peak. She, much like Beyoncé, won't be as in our face over the next few years, but she'll be around. In the mean time, she'll be counting her millions and dropping an album every-other year.
Christina... has pretty much fallen off.

I love her so, but she doesn't even seem to care anymore. She let 'Bionic' die and then spit out 'Lotus' and went back in hiding like nothing happened. I'm sure she'll be around, but definitely not on the same level as Britney or Bey. I'd love for her to get that voice together and have an 'Emancipation of MiMi' moment, though.
Rihanna IMO has proven that she isn't going anywhere - ever. Hate her or love her, she's accomplished quite a lot at a young age and plays the industry well. Surprisingly, she's the youngest person up for debate, but is already 8-years in with multiple honorable records and achievements under her belt. I think her focus for the next few years should be slowing down with her releases and really pushing each album and herself to the limit to further solidify herself as an icon/legend/etc.. Oh, and she's building that empire.
Gaga and Katy have both had great runs, especially Gaga, so I think they just need to stay consistent and they'll be okay.