Killable or unkillable, Neocloudstrife can make it seem as Riku's defeated (bosses don't have finishers). And whether it was an estimate or not, darkhelmet232, it's our best guess.
If you're gonna replace Larxene with Riku, use the Riku boss. We all know what happens if you use Riku from the party. (for those who don't know why, watch this video: http://www.youtube.com/watch?v=oZiHv3TWKX4
