Board Thread:Questions and Answers/@comment-5105419-20131130142942/@comment-6697950-20131130144817

As TUSF said, they weren't mentioned at all after the Grand Quest was completed, so anything said here would be pure speculation. The most likely guess would be that they were just discarded, as their sole purpose was to make the Grand Quest impossible to complete. There is a slight chance that Ymir would reuse their designs for something (why waste money on producing something new when you can recycle old content to reduce develeopment consts?), but your guesses sound completely silly: the fairy cities already have their NPC guards, while Aincrad is meant to be conquered by players, not NPCs. Have you seen NPC armies being used in SAO? Ymir wouldn't be interested in making the 2nd Grand Quest too easy, as then players would lose pleasure of completing it themselves, as well as the fact that it would force them to come up with a 3rd Grand Quest to keep the game running. I can't even imaginge them being used as a boss on New Aincrad, as it would make it impossible to clear the floor, plus someone would already be familiar with their strategy and have an advantage.

The best they could be reused for is some quest.