Interesting Idea for an early BBEG fight

I have an interesting idea for an early BBEG fight and I am wondering what you all think about these ideas.To give you some context, I have been running a West Marches style game for about 1.5 years and the 10 or so players are around level 6 (the levels actually range from 4-7, but most are on the higher end). They accidentally released a demon-man in September and then mostly ignored him since then. He has been growing in power and I have set the stage for an epic 10 person fight. The world is devoid of gods, except the goddess of fate.Here comes the question - I have a couple of options of how this fight could go:1) I have it appropriately difficult and they ultimate win the fight and defeat the BBEG (for now)2) The fight is impossible and they all die and the town they have been building is destroyed, but the goddess of fate intervenes and time gets reset to an earlier time (there is some wiggle room here where most quest lines would be unaffected).The more I think about option 2, I feel like it could be a really cool moment and have the players understand how powerful the BBEG can be, however, this could feel like a cheap shot and I want to make sure the players have a good time.What are your thoughts? Is pulling time shenanigans something that is a cool experience or does this feel like a cheap out that removes player agency?