They'll be as successful as they are now... meaning not very.
Who said? When? I've not heard anything from Fox about a reboot. Especially considering you ALSO have New Mutants to follow, who knows how many films Deadpool or Gambit will get if the first ones are a success, and continued speculation of a X-Force film and a X-Factor series. All the information we have on the X-Films going forward is that Fox intends to GROW the franchise from where it exists right now, not toss it all and start from scratch.
As others have said, not gonna happen. Nonetheless,
I'd expect that there would be limitations on how many films Disney can actually produce (to say nothing of what the market will bear). It would depend on how Inhumans was performing on the screen when they got the X-properties back, but Disney would have to be very tempted to try and tap the X-fandom.
I'd submit they've done a weak, pale imitation of the Hellfire club. If you reboot the franchise, and restore the HC to its original concept as a cabal of ruthless super-0.01%ers out to dominate the world, I'd think you could do a multi-film series with them as the villains. That would especially work if they were low key or invisible in the first film, with the X-Men dealing with the HC's agents, like the Hellions.
To build up on an earlier post, I'd be pretty pissed off if Ms. Marvel becomes a casualty in this possibility.
We would finally see Marvel push the X-men again.This would rejuvenate the X-men. Introducing another generation to the concept of the X-men. The Inhumans would probably be in the position they are in now minus the fart cloud on earth. With 1 book focusing on them.
The only way the higher ups would want Kamala gone would be if her book is no longer profitable, as DrNewGod states. That's not the case right now, and her book seems to have grown in popularity after the release of collections. This is Marvel's most vital new character in years, and they will ride that wave as long as possible. The overall Inhumans situation will probably have little effect on her book.