The attractions in Rivers of Anerica close early on Fantasmic nights, and don't reopen. Early means by 6pm.
All attractions in the buildings connected to the castle close at around 8-8:30pm for the fireworks, and usually open back after 10pm.
Storybook land canal boats close at around 7pm for the night. Alice closes for Paint The Night and reopens. Toontown closes at around 8-8:30 for the night. The monorail also closes about 30mins prior to the fireworks, and reopens after the "all clear".
As you can tell, there are lots of closures every night. If you are not watching the shows, Tomorrowland and most of the west side of the park will still be open. During Fantasmic, lines from Adventureland to Critter Country can get pretty short.