In what situation would you think you can claim for curtailment?
My Dad ended up in hospital in Europe - seriously ill. He was due to board a cruise but couldn't. He was also so ill he was in hospital for a week before he could fly back to the UK.
The insurance company won't reimburse the cost of the cruise. They say his holiday wasn't curtailed as he didn't go back to the UK. 
But he couldn't have gone back to the UK right away - would probably have died on the flight. Policy does not expressly say curtailment means returning home. Suggests/ implies it but is ambiguous at best.