It's probably not a worthy solution, but you could remove dying unit from game and play special animation at the point of dying unit. It looks kinda ugly, but there is no crater.
Crater seems to be triggered by death but it is independent of the unit and death animation. Because when you wait even 0.1 second after death to remove the unit, it removes the death animation of the unit, but leaves the crater for 5-6 seconds. So perhaps it is in its own category somewhere.