Maybe I'm missing something in the story, but I see no obvious way for Cain to know that he actually killed Hebel and the latter will not wake up, heal or resurrect.
How could Cain know that Hebel was actually dead?
Mi Yodeya is a question and answer site for those who base their lives on Jewish law and tradition and anyone interested in learning more. It only takes a minute to sign up.Sign up to join this community
The Gemara in Sanhedrin 37b mentions this exact point:
אמר רב יהודה בריה דר' חייא מלמד שעשה קין בהבל אחיו חבורות חבורות פציעות פציעות שלא היה יודע מהיכן נשמה יוצאה עד שהגיע לצוארו
Rav Yehuda the son of Rav Chiya said that that this teaches that Kayin caused multiple wounds and multiple injuries to his brother Hevel, since he (kayin) didn't know from where the soul departs until he reached the neck.
So it would seem from the Gemara that he happily pummelled away not knowing what would be the killer blow and then when he reached the neck this seemed to be the final, fatal blow that made it clear to him.
Along this line of thinking, also refer to the Bereishis Rabbah 22:8 that notes one view that Kayin witnessed at what point his father slaughtered the bullock and at what point he slew Hevel and that was his marker.