It sounds like a cool idea - the game's climactic encounters might involve the acquisition of fame, fantastical treasure, and ecological collapse. You'd have to get the PCs to have some buy-in for one environment, though. Traditionally, PCs are happy to move on to the next challenge and greener pastures (literally).
I haven't seen a lot of it in discursive RPGs, but Actraiser and Warcraft 3 come to mind as examples of computer RPGs that involve saving the land, killing the rot.
Becoming a guardian instead of a raider is a big pivot for the standard RPG, mainly because it sounds like playing reactively instead of proactively. I'm sure there are ways around that. Just make it seem fantastic and fun . . . and don't recruit any players of Monster Hunter. (Although
this video makes them sound more harmonious than I might expect.)