Yep, OfflineMapTask is mainly used to take the stuff offline, then it's up to the developer to add rest of the functionality. Note that there is also OfflineMapSyncTask that could help to do the synchronization related functionality. We are having a look if we can add functionality there to handle the unregister case as well.
OfflineMapTask basically creates an exploded mobile map package to the target folder which contains all the geodatabases as well. Technically these are just normal files in the device so you can choose to work with them directly if you like. There are 2 relatively easy ways to get them
1) Loop through your FeatureLayers and their GeodatabaseFeatureTables which contains reference to the Geodatabase which has path to the file
2) find all .geodatabase files from the p13 folder (it contains all the packages that we export from the services) that is located in the offline map folder