IMO, Nicki is on her way out, at least in terms of the GP. She's had one hit song (out of a billion singles) during the PR:RR era and it was pop. Va Va Voom did great with no promo or support from Nicki and could have easily gone top 10 if she took it seriously, but instead she's abandoning pop. That's fine at all, but she's known in the GP for her pop songs, so if she's going full rap, she is going to see a drop in her fame.
Gaga's doing fine. She got one (nearly) 4x platinum single and two 2x platinum singles in the US during the BTW era, the album sold 7 million+, and she's going to score a 200+ million gross with this tour.
Only in that they've both alienated large sections of their fanbase. Gaga's established fanbase was much larger so while she took a hard blow, it wasn't a devastating one.
I believe Gaga will have an easier time drawing back casual listeners than Nicki will trying to draw back loyal hip hop fans (album buyers).