Board Thread:Off Topic/@comment-23790511-20150129221847/@comment-3146930-20150130233453

The thing is that most AI only have a 7-year shelf life, but once they die they can be instantly replaced with either the same model or an updated one. Cortana from the series is special because she was created directly from Dr. Halsey, however she does mention to the Master Chief that once she dies, they could just pair him with another Cortana model AI. Not to mention despite Spartans never dying, most tend to go MIA well before their AI would even reach that 7 year mark; this doesn't account for ship AI though.