20-Year Prospect
The federal judicial system is going to be around in twenty years. In fact, there was a 33% jump in crimes that could be tried federally from 1982 to 2000 (source) and those crimes need prosecutors.
Competition will still be plentiful though, as law schools will likely continue graduating more lawyers than there are positions to be filled (source).
There isn't much evidence that the price of law school is going to plummet anytime soon, either. A law school education comes at a high premium and that premium is still on the rise due to competition between schools (source).
A savvy, conscientious, and eagle-eyed scholar will always be able to find tuition breaks, but the median debt of the law school class of 2010 was $105,030. Nine in ten students have to take on debt to attend law school (source). These aren't numbers likely to mystically flatten in twenty years.
You'll have to be just as persistent in twenty years, if not more so. You'll still need oodles of trial experience or judicial experience if you want an edge over the competition. And trust us, you'll need an edge.