depends on the form factor. if 0 - 10% is just an implant or headset, then you would definitely feel alive. but as more neurons get replaced, and the surgeries get more invasive, I think there would be existential crisis along the way. by the time 50-100% gets replaced, there's no guarantee of a containing that many neurons in the same skull cavity, and who knows, maybe ship of theseus immortality comes with immobility. you'll feel alive in VR, but at an existential cost.