I wouldn't worry about ARTPOP under-performing.
A lacklustre era isn't going to kill her. If anything, it will help her in the long run because it'll make her evaluate what she wants and where she's going - i.e. play the pop game for the stadiums, #1s and sales, or follow a more experimental path for creative satisfaction. Continuing to straddle ART and POP isn't really going to work. She got away with eccentricities before because she had hype and novelty, but now that's faded...the reality is that 'full on Gaga' mode is too hard for most to swallow. Team Gaga probably put BTW's mixed reception down to it being polarising, and it's success will have cushioned the blow, but a real under-performance would be an eye opener for them and her. If ARTPOP "flops", Gaga will be forced to fight or let go.
My guess is that she'll fight. Whilst you can tell she's in it for the music, it's also obvious that she craves validation through success (not necessarily charts/sales) and wants a legacy. With that in mind, you can bet album #5 will come hard. And probably quite soon.
I've said it before, but I think part of the Gaga story is going to be overcoming. She's not the girl next door who everyone roots for or the popular girl who people are used to winning - she's an eternal underdog who'll sometimes get the last laugh. We've seen her slay, and then people got tired of the weird girl and wanted to go back to the easy-on-the-eyes-and-ears girls norm. Well, it's only a matter of time before that gets boring again and 'Gaga the underdog' will start looking more attractive. At the moment, people aren't quite at this stage. They're still enjoying the sugar high, and frankly need to see her fall some more before seeing her as the underdog.
A return to form shouldn't be difficult. With Gaga, it'll be a matter of timing and hitting the right buttons. i.e. if she can strike in 2014 with ARTPOP vol. 2 when the competition is winding down, with hitmaker co-created material, great collabs and an easier to swallow image - bingo.
However, the album could do well.
