a) Old links and repos will continue to work thanks to github's recent improvements in redirects: https://github.com/blog/1508-repository-redirects-are-here
b) It's not quite as convenient to commit, but we plan to remain as open as before. If you want commit privileges, you can submit a pull request the usual way, or just ask here (with your github handle). You can also email me if you prefer (address in profile).