Was he punished also for returning on his path?
Malbim: No. "Va'Tashav va'Tochal" teaches that he was punished only for eating. 1 Hashem forbade him only to return from Beis Kel to Yehudah on the same path that he went, but not to backtrack on his path from Beis Kel.
Perhaps we infer that had he been punished for returning, Hashem would have added 'ba'Derech Asher Halachta.' (PF)
Why did He say "Nivlasecha"?
Radak #1: This hints that his body will be a Neveilah, i.e. cast on the road.
Radak #2: Every dead body is called Neveilah, whether of an animal, bird or man, and even a Tzadik - "Nevelasi Yekumun" (Yeshayah 26:19).
What is "Kever Avosecha"?
Radak: It is Eretz Yehudah.
Why did this mishap occur to him? Sheluchei Mitzvah are not harmed, also on the return from the Mitzvah (Pesachim 8a)!
