Every year or two, the queen will get old and the bees will raise another queen to replace her.
That's where the trouble comes in. When the new queen goes out on her mating flight, she MIGHT meet up with a male with killer bee genes. If she does, her offspring will be aggresive. That is how killer bees take over a hive.
A LOT of beekeepers in Texas buy a new queen every year and re-queen each hive. That way, the Queens in EVERY hive are young and of calm parents.
A lot of other beekeepers just re-queen whenever they notice that a hive is getting more aggresive.
Either way works.
Lastly, a lot of beekeepers who collect killer bee swarms simply take the bees home, kill the queen, and provide the hive with a domestic queen. In a few weeks time, the hive is domestic and calm.
Each worker bee only lives for a few weeks. Once the offspring of the domestic queen are hatched and the old bees die of age, the hive is domestic.