This question already has an answer here:
Is it correct, that if the passenger checks in a suitcase - but never shows up at the gate - they have to take the suitcase off the plane before take-off?
Is this a regulatory issue - or is it a company policy?
Edit: I was asking in general, but if an answer requires specifics... :) In this case it was RyanAir flying Malta to UK. They were delayed so much, that it was no longer possible to make the connecting flight (separate booking), but refused to remove the suitcase from the airplane, so my girlfriend could just leave and catch a better flight tomorrow. This surprised me, as I have always heard and believed they will take your suitcase off the plane if you don't show up at the gate.