The monsters in the film and its sequels, such as Dawn of the Dead and Day of the Dead, as well as its many inspired works, such as Return of the Living Dead and Zombi 2, are usually hungry for human flesh, although Return of the Living Dead introduced the popular concept of zombies eating brains.
The lesson is: No one knows what your tonge is going to do. The only way to know is to take it out and see. So you have two options you can hang out at home one day, take your tongue ring out, and try putting it back in every few hours. If it slips back in after 2 hours being out, try 4. If that works, try 6, etc. You can even leave the piercing out overnight if you want to test it.
Generally it will take around three months for a piercing to close up, and this may prove to be just slightly faster for a lip piercing as lip piercings are notorious for closing very quickly. Thus if you want your lip piercing to completely close, then you need to just leave the ring out for this amount of time.