Not all office space is amenable to residential conversion, since the floor area to exterior wall ratio is often much too high for an apartment building (windowless offices are fine, windowless living rooms, not so much).

An office/apartment hybrid might work. I could imagine dividing the building, with offices in the inner core and apartments surrounding the core. The core and surrounding apartments would be totally separated, with separate lobbies and elevators. Although the offices would be totally windowless hellscapes, at least the apartments would have lots of light.