Based on the photos quite clearly showing a feathered port engine, I would dare to suggest that the right wingtip struck the ground/runway during the inversion sequence due to an engine out at go-around, and was not the cause but already an effect.
Am not familiar with the Metro, anybody in the know: is there a speed limit below which maximum aileron force is insufficient to counter the torque imbalance caused by a single engine going from idle to 100% at maximum acceleration ?
1) Why would they be going around from runway altitude with one engine out? Doesn't make sense if you have had time to feather and clean up and you are now on the deck, why wouldn't you land? Think about it!
2) Torque imbalance? What is that. I guess you are refering to Vmc, red line speed, blah de blah. Well again, approach speed is well above red-line speed so if the engine failed on approach, not an issue,. If it failed in the flare...see 1)
3) maybe it is feathered before the accident, maybe it feathered after. Again see 1) & 2) above. If it failed at DH of 200' and they were not visual, then they'd execute a missed from 200' and would not have clipped the wingtip on the runway.... they'd probably have come down short of the runway (Vmc happens quickly, but again see 2) ). If it failed lower than DH then they were visual and would have landed and not been on a high power setting anyway...