If you leave the college, you may want to save your GitHub Enterprise repositories to your computer or move them to GitHub.com. ITS won't delete your repositories immediately after you leave, but once your account expires, you won't be able to access the files.
If you want to migrate your repositories to GitHub.com, consider whether you want them to be public or private. Many assignments from classes should be private because they are derived from textbooks or contain answers to problems that may be used in the future. In addition, make sure you don't accidentally post password or key-pairs as part of your repository.
GitHub Enterprise to GitHub.com
You can reverse the instructions here to migrate your repositories to GitHub.com: https://help.github.com/enterprise/2.2/admin/articles/moving-a-repository-from-github-com-to-github-enterprise/
GitHub Enterprise to Local Computer
You can also download your GitHub Enterprise Repositories by either cloning the repository or downloading a zip to your computer.