The Wiki was always a community-driven resource and as such it it feels like it would have been beneficial to have worked with the community in resolving it’s issues, rather than outright terminating it without any warning.
Don’t get me wrong it was chock full of terrible advice, many articles hadn’t been updated since the original engine launch - some articles were just outright incorrect - but it also contained a lot of irreplaceable information. It will be difficult if not impossible to provide a list of items which were useful without being able to see the original contents. At least we have the Wayback Machine archive.
As for official documentation - the reality is that because it has to be so generic, it’s rarely useful to anybody other than absolute beginners. The engine is well-designed, and I’d argue that once you reach a certain degree of familiarity with it you can find everything you need yourself.
The Unreal Slackers Discord group is by far the most useful place to get answers and help now, but unfortunately isn’t good at holding on to persistent information. Even the C++ Programming forum right here is full of questions being answered with terrible advice.
The Wiki helped to fill that gap, as it covered a lot of problem-areas the engine has which Epic are never going to do documentation on. For example, the sheer degree of suffering you have to go through to get a dedicated server working on Steam.
Glad to hear it is at least backed up somewhere. We do however need a community-editable, persistent source of information somewhere. If Epic don’t provide one you can bet the community will end up hosting it’s own somewhere.