github
For instance, there is a repo called foo.
There are three forks of it called foo-bar, foo-baz and foo-baq which were created sequentially.
foo is updated quite frequently. Forks are more or less outdated, e.g., foo-baq is the freshest one (but not as fresh as foo) and foo-bar is the oldest one.
What happens when the owner of foo deletes it? Which of the forks is chosen as the main repo (i.e. shown as "forked from" in two other forks)?
You can try and reverse how pull requests happen.
Issue a Pull Request
By default this will be your fork on the right (head repo) requesting to push its commits and changes to the original repo (base repo) on the left.
Click the drop down for both base repo and head repo and select each other's repos.
You want yours listed on the left (accepting changes) while the original repository is on the right (the one with changes to push). As illustrated in this image:
Send the pull request
If your fork has not had any changes, you should be able to automatically accept the merge.
If your code somehow conflicts or is not quite clean enough, then this will not work to update via the GitHub web interface and you will need grab the code and resolve any conflicts on your machine before pushing back to your fork.
You should be able to just pull down the other repo and have it merge with yours.
git pull {url-of-repo-with-commit-you-want-to-merge-in}
This will fetch the repo mentioned and have it automatically fast forward merge in any commits you don't have into yours.
So in your example, while on your master branch, or if you want to test it out on some other branch:
git pull git://github.com/dantipa/history.js.git
remote: Counting objects: 9, done.
remote: Compressing objects: 100% (1/1), done.
remote: Total 5 (delta 4), reused 5 (delta 4)
Unpacking objects: 100% (5/5), done.
From git://github.com/dantipa/history.js
* branch HEAD -> FETCH_HEAD
Updating e84ad00..e2d5251
Fast-forward
scripts/uncompressed/history.js | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
Now with the other commit merged with yours you can push back up to your own remote with that extra change.
Best Answer
Provided that the main repository is public, the oldest fork is selected to become the parent:
Source: GitHub Help: What happens to forks when a repository deleted or changes visibility?
Update #1: Doing some rudimentary testing (creating multiple forks and then deleting the parent), it appears that the oldest fork becomes the parent.
Update #2: I emailed the support team, and this is the reply I received: