I'm not sure what you mean by offline, but, if you write your
db_file to an always mounted location, you should be able to search it even if the indexed drive is not mounted.
The DBs are mlocate format, and don't seem to have enough extra information to be worth a GUI. Here's what I did to investigate (Use the Source, Luke!):
# Where is the locate executable?
type -p locate
# What type of file is it?
file $( type -p locate )
# follow the links
# Which package owns /usr/bin/mlocate?
dpkg -S /usr/bin/mlocate
# I keep sources in this directory tree
# install the apt-src package
sudo apt-get install apt-src
# get the source for mlocate
apt-src install mlocate
# inspect mlocate
# clean up
apt-src remove mlocate