This usage is not very common,
and its needs to be carefully distinguished from
the more common context in which social scientists
talk about sustainability, viz., the social
aspects of ecological sustainability. A war destroying
human society would probably be an
example of social (un)sustainability, and it in
turn may have social or ecological causes. (Note
that these categories are only conceptual devices
for clarifying our thinking; real problems seldom
fall neatly into one category or another.)