20-Year Prospect
With a predicted 11% growth rate, there will be plenty of EdPsych jobs in the future (source). Even today, school systems are searching high and low for talented psychologists. In fact, since the last place most modern students want to end up is back in the school system, the demand for good counselors will only increase.
We don't see schools going out of style anytime soon and people needing a little emotional support here and there isn't on its way out either, so you can be pretty certain this job will be around for the foreseeable future.
So if you do end up working in the school environment the rest of your life, fair play to you. Because let's face it: kids may be awesome, but just like adults, many have major issues. Your prospects here depend a whole lot less upon the job itself compared to your own personal interests. So long as you want this job, it should be around.