RIP v sad news.....
As an experienced firefly owner / operator of both the 160 / 200 & M260 along with many of the other guys on the mil forum - it is always advisable to wear parachutes when performing any aerobatic manouevres, it is also critical to have a full brief and ensure the levels and hard deck for level flight are adhered to, then if it still goes wrong - get out, float about and walk back!
The Firefly is a very safe aircraft and very safe to aerobat, however it will NOT suffer fools or anyone using incorrect techniques.... depending on the weight of the two occupants and the fuel in the 160 and depending on what direction they entered will depend on what happened but looking at photos available full left rudder is still applied possibly meaning a spin the right - going to the right if the engine was at tickover then occasionally it stops, especially if cold / carb icing potential - no real dramas at all - sort out the spin recovery first.... and then re-start the fan.
if you don't get the stick all the way forward to the stop and hold it there..... then it ain't coming out.....
AAIB are well versed and WILL give all the details in time...
Very sad day for all involved for sure and not a great few days for aviation especially after the Norway heli rotor head separation.
Dance with the clouds guys!