So in the aftermath of yesterday’s misadventures, I took the chewed up plastic pedals off the hybrid and replaced one of them with the old pedals from my road bike (basic metal platforms, no cleats: I’m debating getting clipless pedals for it). One came off without incident, and it of course would be on the right side. The broken one was worse than I feared: there’s a wreck involved in the fact that the pedal axle was mated to the crank at angle considerably less than 90 degrees.
So my local shop will re-tap the thread for US$10. I considered doing it myself but it hardly seems worth it.