Given your situation where your client asks you specifically to set an expiration.
Is it possible to request/suggest the client again to adjust the expiration?
In most cases (... always) that the client does not approve... you can publish 2 sets nwd files, the first nwd file will have the expiration date and another that does not have an expiration date (uncheck the expire prior to publishing).
Also I don't think its possible to reset once the nwd file expires, it can never be opened again.( on my understanding this is how navisworks was designed )
Now to a question that got me interested, The NWF expired... I think for nwf to expire is when the user is trying to open the expired nwd file or the nwf is referenced to the expired nwd file.
regards,