The only way to find out was with a quick test where I dropped the phone from a height of about 4 and a half feet and captured the drop with a slow-motion camera. Thankfully I had the Galaxy S10, which has a great slow-motion camera mode.
Check out the test below. I'd advise to expand the GIF to a full size video, and tap the "SD" button on the bottom-right to change it to HD for a better view of the pop-up selfie camera retracting as it falls:
It's a little hard to tell, but the pop-up selfie camera doesn't quite fully retract into its enclosure before the phone hits the ground. You can tell the pop-up selfie camera is still in the process of retracting by the sliver of light reflecting off the selfie camera when the phone hits the blanket.
Still, it might just retract enough to prevent the selfie camera from breaking off, even if it hits the ground at an angle that would prove fatal to the pop-up selfie camera if it hadn't retracted at all.
It's also more likely that the pop-up selfie camera would fully retract if it was dropped from a higher heigh, like face-height where you'd take a selfie from. That, of course, depends on how tall you are.
A case might also let the OnePlus 7 Pro's pop-up selfie camera survive a drop around the selfie camera's enclosure.
via Gfycat