No big deal, just have an Atonement spell handy. Have just one Druid teach it to a linguist/polyglot/language teacher, then have the teacher teach it to more people. Soon enough, you'll have a whole community of Druidic-speaking non-Druids. So there's no real issue teaching more people.
And it's not exactly inconceivable that a Druid might teach it. I mean, Paladins fall like rocks, and they're supposed to be the most devoted guys out there...