Other passages in Joshua and Judges indicate that the complete destruction of some of these people groups was not completed until sometime later. For example, Hebron (Joshua 15:13–14; Judges 1:9–10, Judges 1:20) and Debir (Joshua 15:15–17; Judges 1:11–13) are mentioned later in the book as still needing subjugation. Since Israel did not occupy these cities immediately, but returned to their families and livestock at the base camp in Gilgal (Joshua 10:43),1 there would have been time for people to reoccupy some of the towns mentioned. Perhaps some of the Canaanites fled from the fortified cities before Joshua and his army came, and then returned once they left.
40 So Joshua struck the whole land, the hill country and the Negeb and the lowland and the slopes, and all their kings. He left none remaining, but devoted to destruction all that breathed, just as the LORD God of Israel commanded.