Talk:Updates/@comment-27647760-20171203163546/@comment-99.225.85.245-20171227045928

"Eorl led his men in pursuit, and so great was the fear that went before horsemen of the North that the invaders of the Wold were also thrown into panic, and the Riders hunted them over the plains of Calenardhon."

The Return of the King LotR Appendix A, Annals of the Kings and Rulers: The House of Eorl

So the Balchoth weren't exterminated, but the the warriors at the battle probably were destroyed/nearly destroyed.