If I destroy my Keepers' Knapsack and Outrider's Satchel on Aradune, can I rebuy it to claim on Mischief?
No, not if its 1 per account They are making 2 new ones for Mischief theme though that you can buy instead
It will be a news article along with the Halfling Heritage Crate sometime before launch (possibly also include a date when the current bundle and pack stop being sold)