Sent this during the Halloween event - I would assume that you can still loot the seasonal rings and other goodies that went along with them.
Hi DeadEye,
Thank you for your support case.
All but the Unique items will remain in the Strongboxes after the event is done assuming the Unique items drop during the event.
But other than that all items will remain active in the boxes and they will remain in your inventory.
Take care and best of luck.
Kind regards,
Ulf | Entropia Universe Support