Not a problem - you can no-show a flight you book with fully flexible tickets (in fact, the reservation for the seat doesn't necessarily have to be tied to the ticket - sometimes the agent will simply put "ticket holder" and not bother with the ticket number as long as it's Full Y) and the ticket will be still valid for travel, 1 year from original travel date, and still eligible for refund even a while after the ticket expiry (3 or 6 months).

But generally, one should try not to no-show a flight if s/he can help it. Even calling up 1 hour before departure to say you're not turning up, might save someone who is on standby a lot of anxiety