The question isnt wether a CBG is detectable but how practicle 500nm ranged SSM's are considering that the only way targeting quality track data is achieveble is to have a platfrom in line of sight to the target and transmit the data back.
One approach is what was used in the P700 Granat / SS-N-19 Shipwreck.
Initial target location (launch vector data) is provided via SATCOM to the launching platform by satellites and recon aircraft. These also keep providing mid-course guidance to the missiles.
The missiles are salvo-launched, and on terminal approach communicate target data to each other. As i understand it, not all missiles would use their active seekers, instead one (or a couple) take over a "targeting" role, and provide info on the target (radar, radar-reception, IR) to the entire salvo of missiles. If the "targeter" is shot down, another missile would take over its role.
Of course these missiles would still be very vulnerable to SAMs due to their ballistic terminal approach path.
A modern approach could see a "pack" of long-range seaskimmers, of which a few would rise to higher levels occasionally during approach and engage in a similar targeting role, while the rest of the pack would autonomously choose somewhat different approach vectors based on the received target data until the target is within the missile's own terminal range.
Additionally, there are some missiles that don't have to hit the target but just get close enough to release a homming torpodeo.
Except these a) are usually lightweight torpedoes and b) would tell the target the exact approach vector in order to take the usual countermeasures (evasive maneuvers, stealthing, decoys, active systems).
