Albert Barnes Commentary 1 Kings 11:16

"(for Joab and all Israel remained there six months, until he had cut off every male in Edom);" — 1 Kings 11:16 (ASV)

Every male in Edom - that is, every male whom he could find. As did Hadad and his company (1 Kings 11:17), so others would have escaped in various directions. The Edomite nation was not destroyed on this occasion.