Originally posted by Siegmund
You left off the option I consider most likely: eventually being replaced by our own evolutionary successors (and for the first time in Earth's history, there's a big question whether they are going to be carbon- or silicon-based life forms).
I'm with you, but with a slightly different angle. I think most people will deliberately replace themselves with something silicon-based.
Imagine that you could integrate a computer board right into your brain so that you could just think questions at it and "feel"/"hear" the answers, and that this could be done without disfiguring you. I suspect that this will eventually become possible, and then popular.
Meanwhile, AI may progress to the point where artificial systems can perform as intelligently as we do. There are a lot of arguments that claim this is impossible -- for example, pointing out that we are analog systems, not digital (true but irrelevant) -- but I doubt they hold water. As soon as that happens, some people will trade their on-board computers for complete replacement of the brain with silicon.
Suddenly, your philosophical views will literally and directly take on life-or-death importance. For, critics will say (rightly IMHO -- and here is where some of the above arguments are no longer irrelevant) that these people are not just changing themselves, but killing themselves.
At first, the critics will be the majority. But the "new people" will look and act just like regular humans, only smarter. Acceptance will increase until only a few hardliners, with an almost "religious" faith in their ways, refuse the technology.
The Amish are still with us, despite their immense technological inferiority to other groups and despite -- or perhaps because of -- their pacifism. If other groups wanted to eliminate the Amish and take their resources, they could, but they don't want to. This fact holds immense hope for humanity.