Are you saying they can't evict the office tenants in order to convert the building? I'm sure any transition from office -> condos will be long, messy, and expensive. Still better than dead, empty cities though.
IIRC (it's been awhile) most office leases are for 5 years, or maybe 3.. I forget. Not sure if they'd have any stipulations to allow evictions in an instance like this.
I would imagine if office buildings offered tenants a get-out-of-your-lease-free card, they'd jump on it. Office leases are not cheap, and go on for years (last one I dealt with was 7!). And if the office is empty...
The set of laws is different for office buildings and apartments.