Why should we assume they would fear power loss? The fear of death is deeply rooted in evolution - it help organisms survive and prosper. An AI wouldn't be a product of evolution, and wouldn't necessarily fear for its own existence unless programmed to do so. Of course, from our human perspective, it's hard to imagine a sentient being that doesn't give a sh about its own existence, but that's perhaps the attitude we should expect from an AI without an evolutionary origin.