You are talking about computers — the substrate — not software. There is, I feel, literally nothing you cannot do with software. We may not have figured something out just yet, but the sky is the limit. Obviously, always within the confines of some computer. Although the latter is already quite fluid as a concept. DNA strands binding and rearranging have been fashioned into primitive algorithms. Injected into your blood they could monitor, say, your blood sugar level and release some insulin on demand. No plug to pull there, I’m afraid. Once you know about software, you’ll start to see universal computers anywhere. All that is required is a state change we can somehow manipulate (a transistor equivalent).
But, you are right. The dependence on power makes computers extremely vulnerable.