1) Regarding connection we see between brain states and consciousness, how do we know that people are really "unconscious"? What if they're still experiencing and feeling things, but are just incapable of communicating this to us at the time, and are incapable of remembering it? Sort of like how when we are asleep and dreaming we're conscious but we could only confirm this is we wake up at the right time (actually, I'm not sure if this is actually true).

2) Assuming that the connection between brain states and consciousness is legit, then I think you're right. After thinking about it some more, I think the point you make below means it'd be much less than a 50/50 chance.

That leaves open the possibility that consciousness is a physically separate entity for which the brain is the interface through which it moves the body and receives sensation from it, rather than brain processes themselves being consciousness. However most of the ground for that is undercut by the fact that some brain injuries severing parts of the brain from each other also appear to sever the corresponding parts of consciousness -- split-brain observations. It seems that it is not only components of consciousness that correspond to brain regions, but also their interconnection.

We have all this data that says "mess the brain up, and you mess consciousness up". It's possible that there is some underlying thing that represents consciousness, but we have data that says that this thing is messed up when you mess the brain up. It'd be crazy if your brain happens to be messed up in such a way when you die that it leaves the thing underlying consciousness in tact.

But as far as overall likelihood of consciousness remaining, it depends on 1). Could we really say that brain states correlate with unconsciousness? How can we determine unconsciousness?