Mortality rates in this population from pneumonia can go as high as 30%. This is correlated with the presence of other medical problems [lung disease for example], nutritional status and the presence of cognitive disorders such as Alzheimer's.

If you father only has PVD, then his mortality is less than say someone who has heart decrease and obstructive pulmonary disease.
If he is very debilitated, can't get around, can't follow directions, then the rate goes toward the higher end.

Optimal medical care both during hospital stays and outside of course plays a big role.

Specific factors that are important are how good his dental hygiene is, whether or not he aspirates [has a swallowing problem and gets debris into his lungs]
Influenza and pneumoccoccal vaccines help prevent recurrence.

There is no getting around the fact that pneumonia is dangerous for anyone, but especially for the older population.
Are treatments for this are very effective, however, as you have seen by successful treatment in repeated hospitalizations.

Hope this helps
dt
____________________________________
Please click accept to give answer credit. Positive feedback the most appreciated. Bonuses are always helpful. Answers for informational purposes only.