Currently, the dasa of Mercury is running and the antardasa lord is Saturn. Roga bhava was activated by Mars and Rahu (from Aug 2018 till March 2022) earlier and by Saturn from June 2024. Saturn antara will continue till Feb 2027. The next dasa lord is Ketu which is forming a Grahana yoga with Moon in the 12th bhava.
As per the above, chances of your father returning to normalcy is rather low.
Performing Jala Abhisheka for Lord Shiva with proper sankalpa for his recovery will help.