Can one edit a 360 degree video into a traditional video?
I don't think there's any currently way to combine 360 playback and normal non-360 playback into a single player.

More generally, you can convert between rectilinear 360 videos and normal video.  The issue you will have is quality, because the resolution of the Ricoh Theta S is maximum 1920x1080 pixels.  This is HD spec for a normal video, but don't forget that the pixels are being used to cover the whole of a 360 sphere.  When you convert back to "normal" video, I assume you will only want a small portion of that sphere, otherwise the image will be very distorted.  

If you're making SD videos, the quality should be reasonable, depending on how much of the viewing sphere you want to use.  

You can convert between rectilinear and normal videos using something like Skybox in After Effects.  (There are many other ways to do this, but this is the one I have used successfully).