BS”D
Call it what you want, but unless I have to deal with the state bureaucracy when I visit E”Y, I don’t need to desecrate the shem hakodosh of Yisroel by associating it with the medine. However, that is my personal practice and I don’t care nor have I the right or knowledge to care if someone wants to use another term.
Regarding why there is no 8th Rebbe – it is a little off topic but my own feeling is simple – there was and is no one to appoint, and appointing the wrong one would be a disaster for Chabad not only as a Chassidus but as a worldwide organization. The one physical descendant had no interest and was at odds with Chabad (and he has passed away so had it happened that he was appointed and had never broken away we’d be back to square 1 anyway). Better no one than more than one or no one who is universally accepted, as that is the very sad situation in another Chassidus that was once so free of anything even remotely resembling machloikes.