Since the range and height when using just a device are now locked to 100 and 50 metres respectively, I am wondering whose responsibilty  a fly away or similar misfortune  further away than that is?

Yours.

The PIC is ALWAYS responsible for the safety of the flight, irrespective of reason

I would recommend you connect your spark with DJI GO 4 as the flight record is saved in app.  Thanks for support.

For now always the operator.

If a fly away or similar misfortune happened, I'll contact the support, provide the flight records to them, they'll submit a data analysis for the accident if the drone is in the warranty period. The flight records are saved in the APP, like the Elektra mentioned. BTW, I don't think you can fly further away than the limitation.