M'y answer feels awkward and is clearly wrong but i cannot find anywhere on the site that deals with when you need to use ici rather than ils n'y habitent plus in this situation... Think it needs là as well.
The help just takes you to ne..plus
Ils habitent ici? - Non, ils ________. Do they live here? - No, they don't live here any more.n'habitent plus icin'y habitent plus