I strongly agree that machines might far exceed us in intelligence without our ever knowing if they are conscious. Indeed, we might even be quite sure they are not conscious in the same way as us.

I would like to note that I think downloading and embodiment of a human consciousness is actually three separate questions.

One is whether a machine intelligence can also be conscious in a similar way to a human. Personally, I am convinced that this is the case and will at some time be realised. At the latest, when we can build a neural analogue to a real brain at full resolution, say about 20 years from now.

Another is whether a conscious mind can be reproduced. In other words, whether not just the architecture can be replicated but whether a snapshot of its state at a particular time can be taken, and whether that state would continue to operate and experience the subjective states of the original. I think this is a highly-qualified yes; at some stage we may be able to image the brain down to individual neurons and lift those parts of its dynamic state which are required.

The third is much trickier. Just consider the possibility that we image your brain and let that image run away happily on a laptop somewhere, but you stick around. A few months later, you die in a freak accident involving, say, a herring and a washing machine. Are you comforted that a backup (or two) somewhere thinks it's you, and remembers being you up until the point where the scanner was switched off?

I don't think this is an at-all trivial question.