This is why I develop on Sourcetree for Github/Travis/Heroku inside a Dropbox folder. It gives another layer of flexibility and redundancy. If Dropbox fails, all I lose is filesystem sync - and one type of restoration - for a short while. (Bluntly, Github and Dropbox provide very similar services for synchronizing code between computers.)

Having a redundant array of independent cloud providers seems the ideal state. This is the most effective way to provide a single source of truth without it becoming a single point of failure.