Never do a scene where the players are supposed to lose. They either won't lose, or they'll be mad. (Exception: If you tell them ahead of time and get their buy-in)

What's going to go over best is definitely going to depend on what your players like. If they get into your narrations, then 1 will work great. I'd avoid 2 and 3 just because they may just feel bad in practice, again depending on your group. I think 5 is my favorite, it can give the other players the chance to really hang it up if they're into that!

4.5 is the best imo. Let them know it's a vision, so they won't get legitimately mad, but don't tell them they're going to die until it happens.

I would avoid running any combat where the party is forced to lose. That would make any time spent on it feel like a waste. A short narrated vision would be fine, but if you want to make this a bigger encounter, you should give the party a goal that they can actually accomplish. I can think of a few ways you could do this:

• The party could locate survivors among the dead to gain information about what happened.
• Survey the wreckage, the party could use investigation skills to look at debris and pierce together what happened. Think, crime scene investigation on a grand scale.
• The BBEG may be showing a true vision of the future, but not a complete vision. Perhaps there is something that the BBEG is trying to hide, such as a clue to how to defeat them. For example, the party could use some kind of magic detection to see through an illususory water fountain and reveal a magic MacGuffin or a person who knows the BBEG's weakness.