THAT kind of “Conversion” is MASSIVELY costly.
It will at least give those buildings a function, since there aren’t people working in those offices anymore.
The conversion would still be cheaper than demolishing and re-building a completely new structure, and with the way most of these office towers are designed, with a strong central column and everything cantilevered out, re-purposing the floors all at once is feasible. Pricey, but possible.
Basically, strip the interior walls out, then start afresh. Run the utilities lines, then away you go.
Yes, I’m over-simplifying, but it’s still better than derelict buildings all over the city centre, no?