I also struggled with the meaning of "en" in this verbal phrase. If this would help--not sure it will: "S'en aller" means to Go Out Of a place. Have you ever heard the song "Dominique" by the Singing Nun?
"Dominique, -nique, -nique, s'en allait tout simplement..."
Since "de" replaces all prepositions except "to," to think of "en" as signifying "out of" might--might--help. Hope so!
I'm currently reading Le Petit Prince in French and I came across this sentence: "Il y a six ans déjà que mon ami s'en est allé avec son mouton." I understand that it is saying it has already been six years since my friend went with his sheep but was wondering
1) what the "en" in this sentence refers to/does grammatically (I understand "J'en ai six" as I have six of them but don't understand the "en" in this context)?
2) would it be incorrect to write this sentence without the "en" (Il y a six ans déjà que mon ami s'est allé avec son mouton)?
The en originally means d'ici, i.e., "from here," but you can really consider it to be part of the set phrase s'en aller. At any rate, en is mandatory; you may not omit it when aller is used pronominally.