This is why I love git (and distributed version control systems in general). For the most part a short downtime isn't the end of the world. When it comes back up I'll push my changes and that'll be that.
Exactly. I'm sitting here thinking "poor GitHub engineers" rather than "oh crap, how am I going to work?" (Though I do wish GitHub Issues weren't as centralized...)
In short, if you have a project's Fossil repo, you can work on everything locally, then push source, wiki, and issue tracker changes to a central repo at your leisure.