This is a bit sad topic, and yes, this has no fixed set of rules. We would know what Astrological combination says about Life and Relationships with Father. No one wants that his or her parents die early; everyone wants to become successful in life in and share the joy with their parents.
But destiny is not always as per our wishes. We never know what is hidden in the future, and what will be the reaction of our action. This is why one should always be polite, humble, and respectful towards one and all and even to those who have done good or bad for the native. Let destiny be the deciding factor not you.
Sun and Saturn share a very strange relationship. They are supposed to be Father and Son in Hindu Vedic astrology. They also share a very estranged relationship even after being father and son. There is a platonic enmity between the two and people having sun with Saturn in some houses in their horoscopes see early demise of their father.
There are some who have a very rough relationship with their father in their teens and later it improves to a good extent.
There are people who have a very good relationship with their father throughout and father is long lived too. In Indian business communities we can see this very clearly.
Sun and Saturn together in 12th house, 6th house, and 8th house may give early demise of father. I am not saying that it will happen but there is a possibility. Below I am giving a chart where the conjunction is happening in the 10th house but the father of the native was short lived. The conjunction in rasi chart and not in the bhava chart is to be seen.
One can see the conjunction happening in the 10th house. Sun is aspected by the 12th house lord from the father. Mars is the 8th house lord which is 12th to the ninth.
Let us take another chart where the native had a very bad relationship with his father and still it is in shambles:
In the above chart Sun if almost at the fag end of Taurus and Saturn is only 12 degrees. The native never had a good relation with his father since his childhood. Here the point to be seen is that the house lord of 9th bhava Venus is aspecting the 9th house and this has given a very good longevity to the father of the native.
Who can forget this horoscope? This belongs to the most famous young politician of a politicial party. His father was killed in a bomb blast. It became a huge task to pick up the pieces of the remains. See the aspect of Saturn on the Sun. The father was assassinated in the antara of Saturn and mahadasa of Venus which is maraKa to the father.
The see this chart too:
Sun and Saturn are conjoined in 12th house. The father of the native dies early.
To sum up, these are not fixed rules but indications. We should not only see the 9th house but also the position of Sun and Saturn in a horoscope to see the relationship between the two.