We work both radar mode A+C and procedurel, with all surrounding unit sectors with no radar coverage.
Usually the "radarservice terminated" should make pilots squawk standard IFR/VFR, more often than not it doesn't.
We rarely have problems with two aircrafts on the same squawk, one within and one outside our airspace, and when we do, we simply change the squawk of "our" flight....
But we're so far from everything/nearest radar unit we can use all codes, and the system we have is not interconnected with others sharing codes and so..