Just when fans are finally thinking that Sword Art Online’s Alicization Arc would last forever, the long-running arc then finally ends. And as the arc ends in Vol. 18, Sword Art Online light novel author, Reki Kawahara made a special promise that Kirito will return.
It was also revealed that the light novels will make their return in 2017 with a brand new arc. The Alicization Arc started back in 2012 with Volume 9, and its story runs for more than half of the series, 10 volumes in all. The Aincrad arc only lasted two volumes, as well as the Fairy Dance and Phantom Bullet arcs, while the Excalibur and the Mother’s Rosario arcs only lasted half a volume each.
Source: Dengeki Online