I've been lucky enough to never have had problems accessing GFWL games. Even after people thought it was getting pulled offline panicked and moved games off it (bye achievements), it still has not died for me. Even recently!
But the Marketplace with DLC and games purchased has been gone for a while. With some other people, we managed to get it back online a few years ago when contacting Microsoft but no response from them for 4 years now. The Xbox 360 services are still working, but no Marketplace.