Don't worry! The seats are still there.
These seats have been blocked to minimize the chance of having to shift passengers to a section closer to the rear of the aircraft in case the flight is not booked full, and thus allow for speedier boarding and departure.
I'm not sure how it will work on the CS side, but I'm sure that a ticket holder would most likely be confirmed on the flight without a seat, and then assigned those seats as neccesary.