Lancelot is indeed alive in this story, he was there during the Lamia incident, (yes there will be a lamia chapter where the Knights and Arthur find out about what happened during the lamia incident, just a little more graphic and s bit more violent. My lamia chapter is a little different compared to the episode.)

Lancelot is alive, everyone except Uther.

Obviously.

Because Uther is a bit of a dick.