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If you are going to the Boardwalk area then your best bet might be to walk over to DHS and catch a bus to WL. It is about a fifteen minute walk. The bus system usually runs about an hour and a half after the park closes so it will depend on what time DHS closes. Other than that, you would have to take a bus to downtown and then another bus to the WL. You could take a cab as well. Sorry I am not sure what time everything is open until.
You can get taxis right from Boardwalk, too. I wouldn't be surprised if there are some camped out outside when the bars close. And if there isn't one there, the CM at the Bell Services desk can easily call one for you.
I also have Checker Cab (the most common taxi I've seen in WDW) programmed into my cell phone: 407-422-2222.