Path Hider

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 piece 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.

I'm in the exact same boat. I'd like to use some of the monster lore and trying to convert the action oriented bosses to be used in PF2e. I'm thinking it would be pretty easy to just treat the Villain Actions as costing two actions in Pathfinder. I think the minion rules would transfer over as well.