Maryjane, thank you for sharing your husband's situtation with the GRACE community. Waiting for test results can be a miserable time, but the PET scan should be helpful in answering if these are truly metastases to the liver from the lung. Depending on how ambiguous the picture is, sometimes a liver biopsy can be helpful but is not always necessary.
Not seeing the scan myself, I cannot comment on the chances of this being the case for your husband. However, the unfortunate reality is that most patients with stage IIIB NSCLC will evenutually relapse either in the lung or outside the lung, so this would not be at all unusual. If he does indeed have liver metastases then his oncologist will likely recommend chemotherapy to try and control the disease.
Good luck during this trying time, and please keep us updated on your husband's situation.