You make a lot of assumptions, e.g. that the AI is, in practice, being thoroughly backed up, and that it's even feasible to back it up online given its size and

You make a lot of assumptions, e.g. that the AI is, in practice, being thoroughly backed up, and that it's even feasible to back it up online given its size and update bandwidth. More abstractly, deleting a day of memories is still pretty close to a form of death. You better believe I'd feel weird if you restored me from a day-old backup. There is a version of me that died, and I never get to remember that day of experiences. Your dismissal of the possibility of killing an AI only applies in a small slice of possible scenarios. Your first argument is a lot stronger.