There was a fatal loss of a DA42 all composite piston twin last year in germany. Apparently it was hit by a lightning strike that caused explosive delamination of the elevator jamming it completely in the process.
That aircraft was relatively new, IFR approved and of course had metallic conductivity mesh inlaid into the composites. So it can happen that a lightning strike is too much for the relevant structure, however it seems to be rare given the large number of flighthours that part- or all composite airplanes have accumulated by now.