If one had a tumor that has been staged at 3a, the typical treatment path is concurrent chemo and radiation with the chemo at a reduced dose until the radiation is done and then a stronger chemo treatment. Then if there is significant shrinkage and no more cancer in the lymph nodes, one may go on to surgery for a possible cure.
Your husband’s doc probably considers the tumor inoperable because of cancer in the lymph nodes, which makes it a system wide problem that has to be treated systemically. Surgery is for local treatment. If your husband had the lung cut out now with the tumor, the cancer would still be in his body.
It is always a good idea to get a second opinion. I would ask for both a diagnosis and treatment recommendation although, I suspect the diagnosis would be the same, especially after the PET scan results are in. You might as well wait for the PET scan results if you are going to go ask for a second opinion.
Don M