Bosses Missing, Razed Fields, Dueling Witches

I'm in a Razed Fields map cleaning the corruption. I got to the end and died at the corrupted boss, but had another chance. When I respawned and went into the boss arena, the two witches, which are the bosses before the corrupted boss, are missing! Now the map is worthless, because I can't finish it.

Also, I don't know if it was a bug, but when the corrupted boss killed me, I have no idea what actually killed my. I wasn't hit by anything, my health just dropped until it was gone. If there was some ground effect or AOE, I couldn't see it.