I think it's unlikely. Github were on cloud, and then moved to their own infrastructure a while back. In fact they have their own provisioning framework and all that fun stuff.

I doubt they will move back to Azure or any cloud for that matter. It's the same story with Dropbox and similar companies. Once past a point in scale, and depending on the case, for example need to control the data security to have certain certifications, it's essential to have your own infrastructure.