20-Year Prospect
Well, there's good news and bad news. The good news is people will always want to build new things, and that quite often means destroying old things first—that's where you come in as the demolition contractor. As long as we'll still be looking to construct things in a few decades, we'll need contractors whose job it is to remove whatever was there to begin with.
That said, the projected growth for the field is below average; only five percent growth is expected between now and 2022 (source). That's the bad news. It makes sense that the required personnel might shrink over time, as the overall idea is probably to minimize the ways to be caught up in the explosion or other demolition practices (and having fewer people around brings down those odds).
Still, the job itself isn't going anywhere. If you have your heart set on the professional level of blowing things up, you can still work your way toward this career—just don't practice your skills on the contents of your mom's flower box.