Question

Which term denotes involuntary loss of citizenship

Answer 1

Expatriation is as best as I can find, although it is possible to be a voluntary expat, so maybe "involuntary expatriation" is best. Exile means forced absence, but you need not lose your citizenship. Disenfranchisement means losing some or all of the privileges of citizenship, e.g. voting, but you are usually still a citizen, e.g. subject to the law.