Seizures after a stroke are not too uncommon, and can present long after the initial stroke occurred. They are due to scarring of the normal pathways in the brain -
I often compare this to an electrical fire in a building with damaged wires. And, at his age, it is not unrealistic to think that the seizures would make him sedated for several days.
The best thing to do in a situation like this is to try and control the seizures with medicines that will not sedate him. In someone his age, one medicine that I particularly like is lamotrigine. It tends to be gentle, with few side effects, if started slowly. You can ask your doctor about that medicine specifically. It could be added to, or replace, the Keppra. At high doses I have found that Keppra can be sedating for someone your father's age.
Also, to be sure nothing else is going on, an EEG, MRI, and MR angiogram could be performed. This should help solidify the diagnosis of seizure, and make sure that other strokes are not occurring.