"I’m happy to announce that Ted Kremenek will be taking over for me as 'Project Lead' for the Swift project, managing the administrative and leadership responsibility for Swift.org. This recognizes the incredible effort he has already been putting into the project, and reflects a decision I’ve made to leave Apple later this month to pursue an opportunity in another space. This decision wasn't made lightly, and I want you all to know that I’m still completely committed to Swift. I plan to remain an active member of the Swift Core Team, as well as a contributor to the swift-evolution mailing list." - Chris Lattner
Luckily, Swift has become much bigger than just Chris Lattner, with many amazing developers involved inside and outside Apple, including Ted Kremenek. While this is a big loss for Apple, I think Swift will be just fine.
This is a good reminder to make sure you don't have that one "star engineer" on your own team without whom the project cannot move forward aka the bus factor. I recommend creating a pairing culture.