Figure this out

If nanobots replaced your neurons one by one with synthetic ones, would the end result be suicide or immortality? (And if it is suicide, at what point in the process does it become so--at the first neuron, the last, or some arbitrary progress percentage?)

If the above process is immortality and not suicide, then it follows that consciousness would persist from one form to another. Consider another process where your whole nervous system is copied as another identical but synthetic instance. Your original self would have to die (i.e., suicide or non-immortality) before the machine one could exist alone and achieve parity with the former result. If the former process is considered immortality, how can this one be considered suicide or non-immortality if the original self would still exist?

Your brain exists in a soup of chemicals generated by the body as a whole, and these chemicals in combination appear to allow for consciousness as an emergent property. You seem to be saying that the nervous system and brain are all that is needed to maintain awareness of self, but there is no evidence of that. The complexity and variables that give you a sense of self are most likely too complex to recreate and at least involve the body as a whole. This is a faulty thought experiment because the underlying assumption (that modeling the human consciousness is possible) is too low probability to consider seriously. To make that leap, one would have to assume our technology has become so advanced that it is indistinguishable from magic and somehow transcends our current understanding of physics. And in that case, anything is possible.