Unless you deleted the map folder, the rest is replaceable.
Use Explorer and delete any remaining LOOSE files from the root of the unit. Do NOT delete the specific map folder or any other folder or its contents.
Now, connect your unit to Home and you should be offered an application. Accept and install it.
Then make an Explorer, not Home, backup of your unit's contents.
If you DID delete the specific map folder, then unless the map was an upgrade from an earlier version (in which case you should still find it on the computer in compressed form here:
C:\Documents and Settings\yourname\My Documents\TomTom\HOME\Downloads\complete\maps\), then you will have to repurchase a map.