The current behavior in BOX when a Folder owner is removed / deleted from the system is the Folder is no longer available.
The process, in my experience, to recover the folder is not obvious, quick nor easy.
I propose the BOX system notify all Folder Co-owners of a pending Folder removal / deletion and allow 2 weeks for the co-owner(s) to determine whether the Folder should be removed from BOX and if the decision is to keep the Folder active to determine the new Owner as well.