it's a lot more complex than just having sun in the 8th... a lot of people have sun in the 8th but don't die early
I think you have to look at things like...
-mars- if it is afflicted or not
-ruler of the 8th (sign/ if planet is afflicted)
-any planets in the 8th house ( the ones closest to the cusp have the most relevance)
-sun - represents general well being
-ascendant- is more physical health
- also the 6th house could have some bearing
+ many more things!
So not all people with sun in the 8th house are doomed. It is important to look at the chart as a whole and not one isolated planet/ placement
and the 8th house can represent things like finances, inheritances, transformations etc