On (almost) all hard disks, the head doesn't drag on the disk - it floats on a film of air. Even if the head crashes, the intertia of a stack of 14" aluminium platters is considerable, and the most likely result is that the head/mounting is ripped off the arm and flung into the HDA housing/across the room.

Unlikely. The platters are a lot smaller for one thing, so they can probably rotate faster without breaking up. And there's likely to be more complex speed control of the spindle motor, so it may not be able to overspeed significantly. I'm not worried about my PC drive suddenly spreading bits of platter through the front of the case.