I just realized something about the idea Hiding had for Hehkeem. If you are using multiple Hehkeem you can start by reviving 2 cost characters and below from the grave and if they are removed with calamity then a second Hehkeem could revive 3 cost characters from the grave. This way if you make sure to not be to greedy by reviving all your characters, then you can recover more easily after a calamity. This implementation would give better control of how much of the graveyard you bring back at any given time.
I was wondering what if Hehkeem costed 5 resources and the pay X when played will only bring back characters that cost X and not characters with less cost. Then you could play him turn 6 for 1 cost characters, turn 7 for 2 cost characters or even turn 8 for 3 cost characters. With this implementation, Hehkeem will not be able to bring as many characters back at once but at the same time the calamity would not have as bad of an effect on the SoA player.