I just love it how people try to blindly predict what the future holds in store. Gaga could still be topping the charts 1,2,3,4, or 5 years from now. Heck even longer than that. I just say let time tell. We can sit around and make predictions, some based off of her sale figures, but predictions are just predictions and may not become entirely true.
One thing that I do know is true though is that as long as she keeps bringing us quality material I'll keep loving her.
TEoG is performing just like a GaGa third single. Were "Lovegame" and "Alejandro" really huge? Her singles aren't that HUGE when it comes to sales. Stop taking "Just Dance" and "Poker Face" as a way to say TEoG is underperforming. Most of Gaga singles are "just successful." Her singles do not see as much success as someone like Katy.
Anyway, GaGa needs to take a break. I won't make a prediction on how long she will last, but there are no guarantees that she will have future success. She appeals to a market that is extremely fickle, she is the type of artist to have huge success early in her career but then fall off the wagon after a couple of successful LPs, etc. GaGa is already seeing a small decline, which should have been expected. It's really hard to top a huge era, and no one should expect her to.
Forever because she never depends on anyone to make good music. She writes songs, then work together with producers, there are plenty of producers that she can work with, after RedOne, Fernando there will be others, she doesnt need Dr Luke or Max Martin like a lot do. What can keep her not being successful ? I see Edge of Glory topping more than half of her previous singles, musically, and its still selling. Judas was an amazing song but it got issues. So whats the matter with GaGa now? She just won 3 Awards from the MTV Japan (which is not easy for international artists there) and just been announced the Queen of Pop. And most importantly, she just said a couple days ago that shes thinking of and already writing songs for her next album while she is going to promo this era for more than 1 year. She said that real work starts now. So BTW, Judas and Edge of Glory may be just trash compared to the upcomings. Lets wait and see.