Yes they should. And as a resut EU compensation at the appropriate level should be paid to all passengers affected as this was clearly a event within the control of airlines who should have planned and communicated much better.
As for extreme weather…….this is what makes me laugh…this was not extreme…….it snows in winter and has done all of my life. It was a single event on Friday lasting 30mins and only about 2 inches, not Chicago style snow dumps. Saturday was 5 inches in an hour but it is was forecast. If it snows from now till February then that might be considered extreme. But not to be able to open a runway for 4 days after such snowfall is simply incompetance.