Hi there, Jenn!
The Cast Members who handle
Epcot's Flower and Garden Festival are incredible architects -- and dismantlers! However, because of the relative delicacy of the topiaries, these items are not quickly taken down and put away immediately following the conclusion of the festival.
The main lecture series, discussions, and presentations will end on the last day of the Festival (as you note, May 20, 2012). But the topiaries usually take a week (or more) to take down and store for next year.
So, yes! It is highly likely that you will get to enjoy some of the glorious floral sculptures when you are on your adventure.
Make sure you take time to stop and smell the roses!
See you later, celebrator,
-Deborah B.