Down for Repairs targets both the opponent and the Attraction, if any. You choose both targets if you cast the spell. If only one of those targets is legal as the spell resolves, you’ll still do as much as you can to the remaining legal target. The illegal target will be unaffected. If both targets become illegal, the spell won’t resolve and none of its effects will happen.

If an Attraction that is not normally an Attraction (probably because it’s a copy of an Attraction) is destroyed, it will go to its owner’s graveyard as normal, not their junkyard.