Well, one dont prevent the other : There was many nobles still alive during the 3rd war, the syndicate was here and still alive and Aliden for that matter, yet the citizens did not consider Aliden (even thought he is legit heir of Alterac) as their lord, because at that point the Kingdom was annexed by Lordaeron.
So Aiden could have been still alive, maybe in a prison in Stromguard, could have died here too.
Well, i dont know because as i said, he could have that pwoer sooner or later, thats the reason why the sons in real life very rarely killed their father, especially in the occidental middle ages (which is the model warcraft humans is) especially when said father was good and loved.
But yeah, when you read the wiki the part from Legion really feels like writen by a kid >< :
“At some point after the death of his friend Terenas,[27] Thoras was murdered by his son, Galen. However, before he died Thoras was aware Galen was the one responsible, and Galen was aware that Thoras knew it was him.[5]”
I dont know, this is like “ho he got killed by his son BUT HE KNEW!!! But his son knew that he knew!!!” Like what? =p