I have Arebith and Nyth, and during battle, I rezz them a couple of times, Demilich is a pain, and suddenly nyths body is gone..... What do I do now? Reload, Command prompt? ETC?

Is this for the solo campaign? If so you usually find your henchmen back at the place the teleport stone takes you.

Hoardes of the Underdark. It is after the reaper token is taken.

Hoardes was the best of it. You had dead bodies, when you minions died, you had to rezz them using spells and etc.