My father had a stroke February 12th this year. He ended up with brain swelling in a comatose situation. How long will it take for swelling go away?

About 3 weeks . Usually brain swelling subsides within 3 weeks or so. An infarction (non viable brain) from the stroke can cause coma if it is in the brain stem or midbrain. Cerebritis from infection can cause coma as well as demyelination which is relatively rare. Repeat imaging on MRI or CT scan might be helpful in tracking the specific region of the infarct, edema, atrophy and Encephalomalacia, or fluid.
Still comatose? If your father is still comatose it is very unlikely to be due to any brain swelling as that would not last this long. Would suggest speaking to your father's neurologist or physician as to the reason for the continued comatose condition. .