CRT and dinner shows are paid in full. If you miss those, you're out the full price, unless you booked the reservation as a dining plan guest...then there is a no-show fee per person.
At Akershus, California Grill, Victoria & Albert's, and special dining packages like Fantasmic or Candlelight Processional there is a no-show fee.
There is no penalty for missing any other WDW restaurant reservation.