Look into the "swim test" and other such endurance tests given to rats, usually in the pursuit of depression medication. Desire to live is absolutely a thing, and it is real and observable.

My basic thrust wasn't about adaptability, but rather that organisms with a desire to live will eventually replace organisms without a desire to live. An AGI who was uninterested in someone reaching the off switch will eventually be outcompeted by a similar lineage endowed with that desire to live. It might fight back or spawn a few progeny before it was felled. And thus evolution would produce AGIs that want to live.