In Dead Rising, what if u wait 'til the zombies get in entrace after 72 hrs?

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In the beginning of Dead Rising, you are in the entrance area of the mall and have to get some more things to block off the entrance so zombies can't get in. This is in the area where that woman opens the door to save her dog and lets in the zombies. What I want to know is what happens if instead of getting more things to help block the door, you wait the entire 72 hours at the entrance?