So, you’re both in heaven and the last person to leave loses, assuming you mean just out of the two of you (since this is about winning a competition against the devil), the devil would leave immediately and win. Are you assuming the devil can’t then claim your soul since you’re already in heaven? Why not just make it “the last one to leave wins” and then you and the devil are in a staying-in-heaven stalemate.
So, you’re both in heaven and the last person to leave loses, assuming you mean just out of the two of you (since this is about winning a competition against the devil), the devil would leave immediately and win. Are you assuming the devil can’t then claim your soul since you’re already in heaven? Why not just make it “the last one to leave wins” and then you and the devil are in a staying-in-heaven stalemate.
I’m pretty sure they meant first one to leave loses (or last one to leave wins) and just had a brain fart.