144-Hour Visa-Free Transit in Shanghai - what happens if I dont use my ticket back?

I have already posted this question, but it seems to have dissapeared.
I am in Shanghai with my valid 144-hour transit permit. I came from Japan and was supposed to leave for Korea. However, I need to get bact directly to Japan. What happens upon leaving China from Shanghai airport? My permit duration is still ok, but I will be travelling to Japan, which is where I came from in the first place. Any help will be much appreciated! Thanks a lot!