I think that if surgery could be performed radically enough to include all of the cancer than there might be a benefit to surgery, however getting clean margins sounds impossible. A partial surgery may help your cat in a mechanical way to breath better.
There are few cancers that are that slow growing, i.e.: 7 years, but what could have begun as chronic inflammation could have evolved into SCC.
Please decide if you would like to try an integrative therapy for your cat, which could include a sparing surgery and the use of holistic or standard chemotherapy agents. The holistic chemotherapy agents I recommend in some cases for SCC are: Polymva (www.polymva.com), Neoplasene (a blood root extract), Hoxsey Formula, Stasis Breaker, Max Formula and Wei Qi Booster (the last three are available at Jing Tang Herbals, but you will need a prescription from your veterinarian).