If you are hiking the crater, I think the East Maui (Kipahulu) unit is closed, so you may want to check if they are letting people exit from the Kaupo Gap side... If not, it probably means hiking back up Sliding Sands Trail... Here are a couple websites:

http://www.nps.gov/hale
http://gorp.away.com/gorp/resource/us_national_park/hi_halea.htm

A check of the Na Ala Hele website shows that most of their trails are closed (probably due to the Polipoli fire):

http://www.hawaiitrails.org/island.asp?island=Maui