No "Owner Succession" feature (a Group 'will') is a flaw that Groups.io (and YahooGroups) share(d).
Every time I've seen one proposed, those who would not use it have railed against having one.
They insist that the workaround of having more than one Owner (who could delete your Group, or demote or depose you and take over your Group) is adequate and acceptable.
Unfortunately that means Groups continue to become 'orphaned' when the Owner (or last Owner) is no longer active (deceased, incapacitated, losses access to their Email address, or simply loses interest).
Michael
Michael Pavan