It is not always easy to be sure about the diagnosis of pneumonia, without a chest X-ray. But, if the physical examination findings are strongly suggestive of the diagnosis, then your father may well have pneumonia.
Two answers to your question: If it has been several days since the diagnosis was made and the antibiotic started and if your father continues to feel better as far as no longer having chills, improved energy, good appetite and no fever, he is probably on the road to recovery from this respiratory illness. So, if he has had pneumonia and but continues to improve, the pneumonia is no longer a threat, but he should take the full course of the antibiotic.
However, pneumonia can sometimes be a sign of more serious disease and, while he is only 49 years old and clinically improving, he should have a chest X-ray, on completion of the antibiotic therapy to make sure that, 1) the pneumonia has resolved or shows signs of resolving and, 2) that his pneumonia is not accompanied, or even caused, by another serious lung disease.
That your father continues to improve, is very reassuring. But if you continue to have any signs or symptoms, for example cough and chills, even if intermittent or any other symptom that suggests that you are not entirely well, you too should have a Chest X-ray and a blood count.
Good luck