People complain about Github not allowing you to turn off issues and pull requests entirely, but I've always seen it as a positive. It means the truth about code quality, potential caveats, and better forked revisions can disseminate freely even when the author disappears. It becomes a spamfest at times, but is still probably a net positive for the ecosystem.
That being said, as long as you still have the discussion tab, auto-deleting all issues by default is not a big deal.