The original plan of just planting trees did not work out as far as I know. But they seemingly switched to using the methods developed by Tony Rinaudo on how to utilize what is left on the land to restore it. There is a wounderful film about him and his work Der Waldmacher . I had the chance to watch one of the early cinema screenings of the documentary with the director Volker Schlöndorff being there to answer some questions. It was really cool.

That fully depends on your definition of what the “reversed” state is. Will ecosystems adapt to the changed climate? Yes. Can temperatures even drop again? Sure. But species lost are gone forever. Ecosystems destroyed will never be the same again. Different ones can develop with enough time and stopping the human interference… But that is hardly “reversible”. That is… natural systems covering up the damage. Going on. Not reversing it.

Depends on your definition of protagonist probably? If I recall correctly in Katamari you are not actually the ball, but the very small prince who rolls the ball around. In the early stages when the ball is small enough you can still see him, but later when you roll up buildings etc. your actual protagonist is too small to be visible.