Druid - Hard to imagine a Druid as anything but a caster with power over nature. We currently don't have an obvious divine caster, so maybe druids will fill this role. If so, perhaps it'd make more sense to call them Shamans? I typically don't like divine casters and holy warriors (paladins), but shamanistic casters have always been cool in my mind. Maybe Wargfolk only?
I think this could be a really interesting idea actually. Druid is I believe an old word for priest, especially when you're looking at Celtic beliefs, so that can be used as a term to describe what we normally associate clerics to be if the Gods of the world are treated more like elements of spirits of nature rather than the pantheons of D&D (or Greek/Norse). Or they can be treated as someone who is a priest of these gods (considering how closely linked gods of certain pantheons are to nature).
Considering the world I don't see why Druid couldn't fit in with that idea of someone who communes with the "gods" or powerful spirits, has a respect for the things more powerful than man, and is therefore able to command some of that power. If it is tied to nature in particular. You can take examples of Thor (Storms), Sol (Sun), Mani (Moon) or even take the elements with gods like Logi/Halogi (Fire) etc and use them as gods who have command with nature, and therefore a druid might be tied to one of these gods in particular and draw power/be granted favour from their gods.
I'd also say that a key thing many people expect from druids in game terms is the ability to have animal companions or shift into animals.
Shaman would work as a name, but I think one man's Shaman is another man's Druid in many ways. Shamans I believe differ in that they are more linked to communing with the spirits and animism/animals. I think in a real world sense they seek answers from them, but you could definitely have them play as drawing power from spirits of their ancestors/totems of animals in battle or for finding information.
Good examples from a game perspective of the difference is druids and shamans in Warcraft, similar in many ways, but also very different.