Silvaire1,
Mode S is not dead or even dying in the US. While the plan is to migrate to ADS-B for ATC surveillance, transponders will still be required. Mode S transponders with extended squitter will be one of the means for ADS datalink (the other being the Universal Access Transceiver) and will be mandatory for operations at or above 18,000 MSL. Mode S transponders are currently required on most aircraft operating under Parts 121 and 135 and are being installed more and more in Part 91 aircraft.