I know it's impractical and can't be done within probably even a day nor a week, but what would happen if someone very rich would like to spend ~1 billion on bitcoins and buy it all?

At first glance looks like it would be the end. Thinking a bit more it suggests that the later bitcoins would be so expensive that even he couldn't afford it, but he would have so much that could make a huge profit out of it.

If there's someone more literate than me in economics, I'd love a detailed and argumented response.