@shafik @chandlerc @meowray this is exactly what has happened in gcc around 10 years ago. If anything learning from gcc mishaps with respect to reviewers and maintainers of areas is definitely to look into. Many folks from gcc moved on and never back filled. Things are finally getting back filled but it will take another 2/3 get to the time when gcc had more than 2/3 main people reviewing patches especially considering these 2/3 people are over half way into their career.
The one thing which will help is training replacements early on. Replacements on reviewers and code which is not getting "some love".
For gcc I have started to push more to remove code that is just not working and not maintained. As one way of solving part of this issue. The other is getting folks internally to do more review of patches. Even if it is just saying this seems correct is ways a good thing.