After completion of the associated quest, if you have unlocked the entire Hub track, this item can be retrieved from the Quest Item Storage chest at the Quest Point Caravan if lost or destroyed. Otherwise, a new one can be obtained from Draynor Manor.
It is possible to reach the realm using Fairy Ring code B-J-R after you have finished Holy Grail. Some people use this item to help train Summoning by using a ring to reach the realm, then use the whistle to arrive in North West Brimhaven and use the nearby obelisk. Beyond this, there is no need to keep this item after the quest has been completed. As such, it can be destroyed or kept as you desire.