Unlocking seats are not that rare - i had mine let go on rotation in an Aerocommander - a short moment of excitement, but the machine was trimmed reasonably well, and hooking my toes under the pedals let me pull the seat back to the normal position. Helped a bit by the pax in the seat behind.
Made darn sure on next leg to rock the seat thoroughly before takeoff to confirm it was properly on the tracks.