Sagen eigentlich Atheisten auch „tschüs“ (< ad Deus)?
Do atheists also say “good-bye” (“God be with you”)?
Les athées disent-ils aussi « adieu » (« à Dieu »)?
I’m guessing that the semantics have bleached so much that most people don’t realise the origin and simply use them as neutral parting phrases; probably much more so in English and German than in the Romance languages, where the pronunciation has also changed to obscure the origin (especially in German, where the phrase is based on Romance, rather than native, roots).
I’m also reminded about my post on using “dial (a number)” with dial-less phones as well as “drehen” (literally, “turn”) for the process of shooting a film (which often does not involve literal film any more, either).