Ayanami Rei considered herself disposable, but she was literally disposable.
All the Reis shared one soul, as well as some of the memories. You could kill
one and have another ready. The only time when anything like this happens in
SMJ is to Faust (and _maybe_ the other country rulers). Ordinary people are
individuals.
It's also clear that in SMJ they can and do produce offspring by combining
several people's genetic material (otherwise you'd only ever see five different
physical appearances among all the people in the world). The only one we
really have any reason to think is an exact genetic duplicate of his father is
Faust.