A full brain upload will be possible but only after an incremental upgrade of brain parts. My bet is that we will start with upgrades to memory and other functions. The new brains will eventually assimilate all the memories of the biological bits first. Long and short, we will voluntarily become cyborgs first. Once the biological brain has been completely upgraded to technology, game on! We have now put our “consciousness” into a fully technical being that can live as long as there is tech to support it. Point is, it may never be a thing to do all at once at the end of our days, but rather a thing we do slowly toward the goal of full artificiality.