I had already tested RTH manually on the previous flight, but I had done so in stabilised/atti mode. Turns out the results are quite different in acro - return to home becomes return to ground.
Somehow all that broke were 4 rubber bobbins. The twitching ESCs went into some sort of failsafe mode themselves after the crash and stopped twitching, one by one, so they and the motors were all fine.
We managed to find it by tracking the video signal (at first very faint, but enough to see the OSD coordinates as we got closer, and then the image itself), and by using the discovery beeper of course.