is it with modern civil ATC radar to 'see' a target with primary should secondary go down?
Most centres now use Multi radar tracking as well, PRI returns may be a bit "fragmented" for want of a better word, and correlation lost. As ATC Watcher said, we had the luxury of continued tracking, but I wouldn't habe been happy with say 10 aircraft in the same predicament in one sector. A greatly increased workload and no real guarantee that the tracking continues.
ATC Watcher, we used to be given a contact number to call if this happened; ENDEX. Is this still so?