I went to Network Admin > Sites > clicked on a site and changed the site url for a child site. Now that site is gone altogether and I cannot get it back. What can I do now?
First of all backup the database before attempting anything.
To get the blog to be displayed in the list you have to reverse the following action:
You can do this manually via MySQL:
The users will, unfortunately be gone, due to this in a loop:
...performing even if the tables aren't dropped.
The rest - settings, files, etc. should be all intact.