Basically I stand with the "process it now " camp but I have gotten into this situation before where for whatever reason i needed to use/save the whole roll (eg rare film, short on film, broke). Treat it as two rolls of film. In the dark open the camera cut off the exposed film and load it on the reel and then in the dark fumble around reloading your camera ;-) You will have a hunk of the paper to tell you what is left. Even if you do it smoothly you will loose a couple of shots.