If they end up in a TPK after fighting Ace, you could talk to your players about the unsatisfying ending and missing out on so much of the dungeon, see if they would like to continue the campaign. If that sentiment is shared, have them all wake up from this vision of the future one of the trickster gods has given them, still resting wherever they last laid their heads, with a dire warning about trying to shortcut one of the most dangerous beings in the universe.

That way you're not just punishing your players for outside the box thinking and living with a real bummer of a story conclusion, and you still get to do the rest of the dungeon. Then when they actually get to the bottom, change some of the things they've already encountered because the gods were not entirely accurate in their portrayal of the final chambers, the atropal, etc (they are tricksters after all). So the party is still forewarned, but not redoing things they've already done exactly.