We are deploying Collector on Getac T800 Windows 10 tablets and Garmin Monterra Android-based handheld units. In this deployment, we are loading a tile package of a USGS topo for our entire state.
On the Garmin (Android 4.0.1), you can continue to pan around beyond the extent taken offline (features and basemap) after you switch to the basemap on the device (the .tpk).
On the Getac (Windows 10), you can't pan much beyond the extent taken offline after you switch to the basemap on the device (the .tpk).
It is important to be able to use the tile package basemap beyond the area taken offline in case a user needs to collect new data "on the fly" beyond what they checked out in the office.
I am just posting this in hopes that if this is a bug, it is fixed for the next release.