消えてしまえ vs 消えちまえ

Listening to a song, the first chorus uses 消えてしまえ to describe emotions fading/disappearing/vanishing, but the final chorus uses 消えちまえ instead. As far as I can tell via translation apps/random forum posts, they both mean "disappear" (with しまえ adding a sense of finality?), but I'm wondering if there's some subtle difference in meaning between the two?

A) are they actually the same word/phrase conjugated differently, or just two similar words/phrases?
B) How does the difference change the meaning or implications (if at all)? formality, timing, passive vs active, statement vs command, etc.?