Just imagine that, in the normal course of things, a person at time t is constantly being copied into a slightly different new person at t+dt and then destroyed. There is a causal connection and thus an inheritance of memories, but not single "essence about yourself" being conserved.
With current technology we only have a directed linear graph, like o -> o -> o -> ... . With uploading tech this graph will fork into two paths, but neither of them can claim to be "the original", because there is no such thing.
I mean, maybe this concept of "personal identity" is simply wrong. It's an illusion because currently threads of causality on people are linear, but that's just a technological limitation.
And I don't see how linearity has to do with self-preservation instincts. Maybe you are arguing that once we have several diverging copies the self-preservation instinct will change and be content as long as one copy still survives? I just can't imagine it.