This is a solution to a non-problem. Hosting taken down git repos is easy an due to gits design all developers already have the source code. The real problem is hosting issues and PRs in such a way. Github has an API and it's possible to script the backup but source code gets backup automatically so when the takedown strikes it's not a big problem.
https://www.fossil-scm.org/home/doc/trunk/www/bugtheory.wiki