According to this thread
you don't have to use up the free heroic character during the anniversary period. It is there to stay and you can delete it and try another toon if you like.
Prathun, post: 3883027, member: 5349 wrote:From JChan:
You are not required to redeem the Heroic Character within the promotional period. You will get to keep the credit as if you paid for a new Heroic Character.
Prathun, post: 3883039, member: 5349 wrote:From JChan:
Yes, you can delete the Heroic Character and still get credit back for the Heroic Character, however you will not receive the items from the Heroic Character Consumables Pack again (Platinum, Bayle Marks, Food and Drink).