Board Thread:Show-Related Questions/@comment-64.136.205.182-20170220062643/@comment-27794543-20170221041632

Mountain Men created Reapers from Grounders using the "red drug" and psychological conditioning. Withdrawal from the red drug is fatal, as was shown with Lincoln (Abby restarted his heart with shock sticks). The Mountain Men were killed at the end of the second season, so there wasn't anyone to create or administer the red drug. Thus, it's likely that any remaining Reapers died of withdrawal. If any survived withdrawal, they could've gone back to their old clan. To read more, see Cerberus Project.