Can you expand?
Open Source resources need to be maintained at a financially remote entity. The worst thing than can happen is that the principle development group goes bankrupt or gets frustrated, says "we're done", turns off all of their servers and disappears. No more download site, no more source code, except whatever individuals have stashed away. No more forums containing 10+ years of discussion. All gone. Part spite, part "we just don't have the resources to maintain availability."
The whole arduino .org/.cc split could have gone that way, pretty easily. There have been complaints (here) that the 1.7x IDEs supporting some of the .org-specific boards are no longer available for download. (they're still on github,)
The older EAGLE binaries almost disappeared when Cadsoft was acquired by Autodesk. The HTCC "free" compilers went away when Microchip acquired High-Tech. The Mac versions of Codewarrior stopped when Motorola (Freescale?) bought Metroworks. (These last free examples were not "open source", so they weren't "ideology" crises, but they were unpleasant enough...)
Note that Arduino already survived one "we don't want to run a OSSW site any more; stuff used to be hosted on Google Code...) Microsoft could ruin github, but it would pretty much have to be a relatively slow process, giving plenty of time for a transition to something else (assuming that there IS something else..)