I don't think they "die" but instead fail because they are full of errors as a result of the Covie copying program. Cortana remarks that the copy she gives to the Spartans will not be as good as the real her, and as a result the copied Cortana thinks she needs more help so she starts to copy herself over and over then those copies copy themselves, hence the "flood" of Cortana transmissions on Unyielding. She had to make a copy of herself just to speak to the Chief.writer87 wrote:also, i remember reading the AI copies would die soon after, and furthermore the AI's like Cortana only have a seven year lifespan before they are likely to succumb to rampancy. Thus, they have to be deactivated before the seven year mark.
Cortana is a a Smart AI that has a 7 year life span because after that period they begin to "think themselves to death."