In 1e Warhammer, there were three spell casting career paths - the Wizards (of all their different kinds), Priests and Druids. While both wizards and priests have changed and been polished/focussed, druids seem to have been totally discarded. Is this the case, do druids no longer exist in the Old World, or will they be gracing us in a future FFG release?

There are 2 Colleges focusing one on the Beasts and one on Nature/Weather. There is also Taal's Church.

If you mention the Old Faith, i've seen mentions, maybe more details in Signs of Faith, or it's for a later date.

From my limited WH lore, "True Druids" in the current incarnation of the gameverse only exist in Albion. This was revealed in the "Dark Shadows" campaign, you can check the wikipedia article which is quite complete.

As Cwell2101 said, you can play a nature focused spellcaster either by joining the Amber order aka Shamans or the Jade order aka Druids (both in the Winds of Magic supplement), but you can also play priest of Taal (Signs of Faith supplement), the human god of Nature. I'm afraid that there is no way to play a Druid-like character in the Core set.