If you don't use it after a while it hides and you get a gray bar above the top row of letters. You should be able to swipe up in that gray space and bring it back.
Are you sure that it automatically hides if you don't use it? There had been a number of times that I accidentally hid it because of my typing habits and the way my fingers were moving.
But doing a little flick up or flick down will show it and hide it, respectively.
If you don't use it after a while it hides and you get a gray bar above the top row of letters. You should be able to swipe up in that gray space and bring it back.