You can either deal with the occasional non-productivity from a SAAS offering (which for GH has never lasted more than ~half a work day), or you can spin up all your own stack on-prem and generate 10 additional full-time problems in the quest to solve this one periodic issue.
The trick is to never put yourself in a position where your tools absolutely must work immediately or you lose a customer. Why make a promise on delivering a piece of software until its already in hand? Also, if github goes down and I really wanted to get an issue comment in, I can just open a text editor and keep a note around in my local repo until everything is back up. I can even do some crazy things, like share my local branches with other developers over side channels until things get back to normal in the centralized system.
Wasn't this kinda the entire point of talking developers into moving to the git model? Would be fun to rewind the clock and use these takes as an argument for sticking with TFS, et. al.