How much time does a person have with stage 4 esophagus cancer?

My dad has been diagnosed with stage 4 cancer of the esophagus, it has spread to his upper back, in his right lung and his lymph nodes.. The doctor says it is terminal, but they have given him chemo and radiation to help shrink the tumors (the tumor in his esophagus has completely blocked his esophagus and he now has a feeding tube).. He really hasn't told me how much time the doctor has given him, and I would like to know.. I am enjoying every minute I have with him just as if it was the last day.. What do you think??