I'm not a lawyer, so this isn't legal advice. But, first, read the lease and see if there are any provisions in there in the event the apartment is, or becomes, inaccesssible or uninhabitable. The lease itself may specify something, such as prorated rent for the month(s) in which that occurs.
Second, if the lease is silent on that, first find out what the law provides. Then, armed with that information, either: (1) try negotiating with the landlord, or (2) have your lawyer conduct the negotiations. Unfortunately, at several hundred dollars an hour, you'd probably end up paying a lawyer more than you'd save via a successful negotiation. Nevertheless, those are some of your options.