Get deleted groups API should include members as well.
When using the list deleted items API (GET https://graph.microsoft.com/v1.0/directory/deletedItems/microsoft.graph.group) I would expect to be able to use $select with members, and getting them as well
The reason to get members as well is, in case of tracking users details, and membership to groups. Once the group is deleted, there is no way to know which users/groups were part of its members. Therefor, there is a need to pull all users again.