To expand a bit...
Most GA owners (not flying in Class A / FL180+) will probably keep their existing Mode A/C transponder and install a completely separate 978 MHz ADS-B "out" transmitter, or a 978 MHz ADS-B transceiver (UAT). So if their ADS-B goes out, they'll still have their original Mode A/C transponder.
Most large commercial aircraft will probably get a 1090 MHz ADS-B transceiver to replace the existing Mode S transponder. Loss of the ADS-B transceiver would typically mean loss of Mode S capability as well.