Death happens because the neurons in your brain undergo necrosis extremely fast without oxygen and that is pretty much responsible for everything you are. However it is theorized that you can extract data from them for a much longer time than the critical time needed for brain death, but that process cannot occur naturally.
But probably that would not a very stable/reliable business either so my only faith in this is transhumanism.
I wouldnt think its really you after you die, brain is so complex that even little changes there, change whole person. Same as on ME2 like topic starter said, they dont even know is it shepard or just remnats of his memories and life
Besides, how do you handle that you know you have died and have memories of it? I think it would drive anyone insane.