If an Admin (or Super Admin) of a group leaves chess.com, and no other member of that group has Admin righst, can the group be deleted, or how can another member take over as Admin

The group cannot be deleted.  But If someone wants to take over someone should contact kohai and tell her the problem and she can make who ever want to take ove a SA, or you can put a ticket in to the help and support and explain the same to them and they can make whoever takes over SA for the group.

Thanks Terry, will give it a try.