20-Year Prospect
The good news is history isn't really going anywhere. That'll still be the case in twenty years, when today is part of history. It keeps happening every second (mind=blown). Twenty years from now the biggest difference is there will be twenty more years of history to put in a notebook somewhere.
That doesn't mean there will be so many historians doing all the notetaking, though. The Bureau of Labor Statistics predicts that employment in this field will grow a whopping two percent over the next decade (source). Even moss grows at a faster rate.
This field will be around as long as time goes on, but as record-keeping improves, the amount of jobs available are going to shrink.
If you want to guarantee your place, you need to find ways to use technology in your work. For example, historians are using digital mapping to find ruins and examine dig sites. Some sites are so overgrown that they're in danger of becoming lost (which is why we need you to beat the moss).
The new technology is key. Not only will it better aid you in your work, you've also got to bring something new to the table that all of the old and established historians don't have. That'll be your ticket to breaking in.
Or, you know, smarts and really great people skills.