Paul Farquhar
Legend
If a character decides they don't want to be of a given class anymore, you wouldn't use the multi-class rules for that. You know, because those rules don't actually remove the class in question? However the player and DM decides to mechanically and narratively enable the change from druid to fighter (and this would be a custom thing, as there's currently no rules for doing such a thing in the books if I recall correctly), the end result would be that said character would have some levels in fighter and no levels in druid.
Sure you could do that (although, speaking as someone who has had several different professions, one doesn't immediately forget everything you learned just because you decide to do something different). The point is, there are no RULEZ for it*. Nothing on changing or removing a class. Nada. Zilch.
What gets me is the hypocrisy of people who want to burn people at the stake for interpreting something differently, but are quite happy to invent rules wholesale in order to support their position (very much like RL religion).
* There are optional rules for changing subclass, and I could see value in creating an oathbreaker druid subclass similar to the oathbreaker paladin.