I get the feeling you are really asking about what happens to your existing group at Yahoo. The answer is nothing. Groups.io just makes a copy.
When my group was transferred I immediately put the Yahoo? group on moderated status, and I edited the home page to point to groups.io. It has been over a year and the Yahoo group is still there, unused. If you want the Yahoo group as backup it will stay there until Yahoo goes belly-up.
Tom Link