Had two dremora lords on an ancient dragon, it started to eat one and the other dealt a final blow to it. It interrupted the animation, dragon died, both dremora lords alive.

Wondering now if a summon or companion can save the PC from this, would be an ... interesting ... experience.

Any of the kill animations can be interupted and cancel them out. Ive had it numerous times when close to world objects with every type of enemy.