…as a further response, what you should be worried (or at least give consideration to) is that the Council could withdraw its Occupancy Certificate and/or that the Owners Corporation (O/C) could require its Common Property (ceiling) to be returned it its original state.
I’m also a conservative, but as the works have apparently been professionally undertaken and the current Owner of the Lot has a Structural Engineer’s Certificate, the chances of the Council or the O/C taking any action is remote in my opinion.
I’m not a lawyer, but why not ask yours to request an extended cooling-off period or depending on their advice a delayed settlement, either one being conditional upon the vendor obtaining either or both of the requisite consents?
Personally, I’d focus on the O/C’s consent, but be guided by your legal advice and in the event that the vendor doesn’t agree, then that’s likely because they can’t obtain those consent/s, in which case you walk away.