Well back to the original poster, I hope for the best man.
My ex and I had a few scares like that. She was on the patch and still came a few days late a couple times...deffinately scary. All you can do is wait it out though and see what comes. There's no magical crystal ball that I can look into and tell if you're buddy's going to have a kid so all you can do as a friend is hope.
Try not to bring it up too much, take him out to grab some coffee, reminise about old times, go play mini golf, go get drunk - whatever it is that you would typically do given that he were not in this situation. That will keep his mind off the "what ifs" and make it so the issue isn't confronted unless it truly becomes an issue. Chances are that she's not pregnent and he's going through a mental hell for nothing (it is deffinately hell wondering), so try and alieviate that hell for a bit.
Now, if it does turn out she's pregnent, be a supportive friend and help him out where you can.