Sunfish, radar use and coverage in the new system will be exactly the same as in the current system. Why would you think such a fundamental feature wouldn't be included with the specification for the new system? We managed to include it last time.....
The "entire separation schemes, fuel cost savings from reduced separations, direct routings, etc., etc" doesn't break down if there is an aircraft with broken ADS-B. We just have to resort to using procedural separation between that aircraft and any others it crosses paths with. A 1000ft works quite well. The miscreant aircraft with the dodgy ADS-B is the one who will get shafted if he can't be accommodated. Exactly as happens today.
You're confusing two systems. The first is the hardware and software, the second is the separation standards and controllers.
The new system will not be inherently more or less resilient than the current one to failure of radar or ADS-B equipment.
You've been listening to too many Dick Smith conspiracy theories.