God did not redeem angels when they sinned, but cast them into hell. With man however, God always preserves a few. When God flooded the whole Earth He preserved Noah and seven others; Noah's wife, his three sons and their wives. When God destroyed Sodom and Gomorrah with fire and brimstone He preserved Lot, and His two daughters. Lot's wife was destroyed when she looked back.
I personally find this amazing that with the angels God destroys them all, however with man most are destroyed, but He always preserves a few. In every case these few don't deserve it, but God gives them what they need to be redeemed. The ones preserved have this in common; they believed (trusted) the Lord.
Reference: 2 Peter chapter 2