Should be an option to not delete all memberships if a group is unmarked provisionable

There is an option in provisioners to set "Delete group if unmarked provisionable" to false, so the group is left alone. However, it still deletes all the memberships for that group. There should be a similar option to "Delete memberships if group unmarked provisionable", and if false it would leave the memberships as is from that point on. Otherwise, there isn't much point to the existing option, since an empty group isn't very useful