One of the power cards states that you can remove one dalek from each territory of an entire continent. Some of the territories were left completely empty with that power. There is definitely nothing in the rules to guide us. Who would then get these territories?
I guess we'll houserule to say at least one dalek must remain and it only impacts territories with more than one dalek.
I'd say that you do what the card says, and if that leaves territories empty, then no-one controls them until someone gets around to invading them. If you don't want to allow free conquests that way, then either house rule that occupying a vacant territory doesn't qualify you to draw a card at the end of the turn, or that an empty territory is defended by a lone rogue Dalek who you need to defeat to claim the territory.