That Depends. There are a lot of factors that determine survival without treatment for lung cancer: the cell type, how big the cancer is, whether it has spread anywhere, and the location of the cancer. If, for instance, the cancer is in the brain, not treating it would probably cause a lot of suffering. That said, for some people, no treatment of lung cancer is an option. But, you must know that it is fatal.
Depends. Depends on what kind of cancer and what stage, may be from several weeks to several years. Go online or ask your doctor to provide you with the numbers for the specific cancer you are interested in, and bear in mind that every patient is different and the numbers are a range.