A very interesting question indeed.
I do believe it is possible for w human soul to be destroyed but not by a nuclear weapon. I see no reason for one form of energy to destroy another form of energy.
Energy however can be consumed. The same way we consume electricity I believe a soul can be consumed by another type of being. Perhaps this is where 'demons' come into the grand scheme of things? I'm not sure.
A soul is energy. It cannot be destroyed but rather consumed.