These things have short term effects but in the long run it will not be an impact on the cruise industry. Reports are that the Concordia event had a slight ripple effect on new bookings across all cruise lines but really didn't cause more than a blip in cancelled bookings. I think the Costa Allegra event will only be a further impact to Costa and not other lines.
Costa did brilliant damage control on the Allegra event. 100% refunds including a free two-week resort vacation in The Seychelles, plus flights home. I read that Costa had three chartered jets sitting on the tarmac at the airport waiting for the ship to arrive. Half of the passengers took them up on the resort offer and went from the ship to buses to the resort.