The parks will only close if the power fails at WDW (which is did last year during Wilma) or if guests are in danger.
I dont forsee guests being in much danger (except for possibly a couple of hours, where they could close the parks).
Even last year, during Wilma where Orlando got tropical storm winds, the parks closed but opened 3 hours later.
So, just because they close doesn't mean it's for the day. The parks didn't open until 2:00 in the afternoon during Wilma, but then opened after the storm passed, and the day went along as normal, with Wishes even at night.
By the way, the day that Wilma hit and the parks closed for a while.....when they re-opened, and for the next day or two, the parks were DEAD! We walked on whatever we wanted.