Github is on the chopping block as a tool (it's sticky as a social network). The other stuff not so much.
The things that are going away are tools that provide convenience on top of a workflow that's commoditized. Anything where the commercial offering provides convenience rather than capabilities over the open source offerings is gonna get toasted.
Even at recent levels of uptime I think it would be very difficult to build a competing product that could function at the scale of even a small company (10 engineers). How would you implement Actions? Code review comments/history? Pull requests? Issues? Permalinks? All of these things have serious operational requirements. If you just want some place to store a git repository any filesystem you like will do it but when you start talking about replacing github that's a different story altogether and TBH I don't think building something that appears to function the same is even the hard part, it's the scaling challenges you run into very quickly.
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