No, you don't lose DEM (it's incorporated in the maps) and autorouting also functions.
Since Mapsource doesn't support Active Routing you'll have to use Basecamp or your GPS for that.
Put the img and the SQL folder in a Garmin folder on SD (or in a connected GPS) and you can use Active Routing in Basecamp.
The only thing you lose by splitting an img for Mapsource is the ability to search for POI.
There is no official Mapsource version, only an img as download or on SD card.