The corrupted gems being cured is definitely happening; can't say we can see all of the corrupted gems' normal forms.
As for Rose coming back, there's also a posibility that happening. If Steven chooses to live a mortal life, that is to say he wants to grow old and die of old age, that would free up Rose's gem from keeping Steven alive.
I feel that in order to satisfy fans' needs and dreams, they're gonna bring her back, one way or another. Killing off Steven or not at some point of the show might factor in, but there's a good chance of it happening either way.
Steven is not going to get killed off. Although it might be an interesting timeline, that kind of stuff doesn't happen to the main character.
We've already seen plenty of flashbacks of Rose/Pink; I can't say I would be satisfied if she came back. As people have said before, it basically undermines everyone's character development up to this point.
Pink was created as a Diamond, she didn't become one, she was always one.
Pink was essentially a child to the rest of the Diamonds, she acted like one as well. They also didn't trust her enough to leave her on her own where she could potentially waste valuable resources or she gets herself hurt.