I think you are missing the point. The ownership of the domains was changed. At that point, the original owners would have been unable to modify any of the DNS configuration that the new owner specified. For ownership to change back requires intervention by the applicable TLD management organisation.

I agree that the domains were probably only down as long as it took for the respective companies to purchase new names and set the DNS records. Bearing in mind that a DNS change can take up to 24 hours to propagate, an on the ball administrator could have had the new domains set up quickly enough that the site would have been available on some domain all the time. Add a mail-out to all your current users with the new URL and you're sorted.