My uneducated prediction about what's going to happen:
Russia is going to recognize the rebel areas as their independent nations, and secure those areas, and in addition the southern parts east of Dnieper river connecting Crimea to Russia via land.
After that new set of negotiations will begin. I doubt Russia has the will to go further than that, as then the issue of guerrilla warfare will become more of an issue more than it is now. Those south-east of Dnieper areas aren't densely populated anyway, and the rebel areas are rebel areas as of now anyway.
Or another scenario is the same but without connecting Crimea to Russia, but just integrating the rebel areas.
Full scale invasion of Ukraine seems kinda retarded. Russia could do it, but they couldn't hold it for long without bankrupting themselves.
One huge factor that is kinda unknown is the Ukrainian will to fight a guerrilla war under occupation. Will the vast majority of the population accept Russian rule if it means this bullshit will be over with, or are they truly committed to this whole Ukraine can into Wect meme?
That being said, Crimea is lost for Ukraine for good.
It's just too strategically important for Russia, that they very likely are ready to start throwing nukes around over it. For diplomatic reasons Ukraine should keep claiming it, but they shouldn't try to retake it at this point. But those other rebel areas are another story. Ukraine can fuck with them as much as they want/can.