First of all, most Kingdoms in the warring state era did some similar reform, more or less. Qin was the one who did it to the extreme.
Secondly, Qin's legal documents were not well preserved as it lasted short and documents were on bamboo sticks, many were destroyed during the war at its collapse. So the description is mostly based on later historian's books in bits and pieces.
However, the understanding is that the noble titles are directly connected to the achievement and can not be passed to descendants. Not much can be passed at least.
This practice was an extreme during an extreme time. Later dynasties relaxed a bit to for example "lower by one rank every generation" in Qing dynasty so the decedent becomes commoner after 5 generations.
If the emperor and his relatives not killed during battle,were they put to the sword, or banished somewhere with each succeeding generation sliding down the hierarchical rankings until they to became commoners?