They did separate the Dragon at max Q that was the purpose of this test. If the booster has already detonated its not a separation test its a recovery. Separations are done at the onset of a flight abnormally by time the booster has blown up it’s too late. None of the prior launch recovery systems could handle a full booster detonation that’s not.the design point. Think about it if the booster you are attached too has already detonated at supersonic shock wave speed one what is there to.separate from and also is pulling the capsule away at a few hundred miles an hour gonna matter with a supersonic blast wave tearing your vehicle apart come on now think this logically through.
So the emergency separation is designed for what failure mode of the booster? Multiple engine failure (I think Space X has 1 or 2 engine out redundancy), booster structural abnormalities not leading to an explosion? Or ??