If github were to be abandoned for anything, it'd make sense to move code review and bug tracking elsewhere. GitHub does a reasonably good job of hosting git repositories. It kind of sucks at code review and the issue tracker is rudimentary at best. These days you can do "log in with my github account" so if done well, it'd not have to be very painful.

JetBrains make great stuff and they have a code review and repository exploration tool called Upsource in development, which should come out soon. I think it's proprietary but that would be no different to github, and it's designed for self hosting.