> Under emergency conditions, you'd expect the separation to be handled by ATC.
ATC is never responsible for general traffic separation in visual meteorological conditions in the United States.
ATC is responsible for separating IFR airplanes from other IFR airplanes. When flying below 18000ft MSL in VMC, those IFR aircraft are still responsible for looking out the window to see and avoid VFR aircraft who may not be talking to ATC (and to be clear, the VFR aircraft is jointly responsible).
Just to drive this home: it is still 100% legal to fly around in a Piper Cub at 9500ft MSL with no transponder or radio in most of the country. It is legal to fly around VFR in a jet at 17500ft squawking 1200 not talking to ATC almost everywhere in the country. Primary radar coverage is going away, not getting better. You have to look out the window.
