(copying what I said on the library team mailing list)
Wow, Alex, I'm so sad to see you go! Well, I know you'll still be
around, but still. Your leadership on the libs team will certainly be
missed. With that said, I'm happy for you that you're prioritizing
your needs. 
You've been an inspiration to me with your work on Rust, and a stable rock as someone I've always been able to ping and rely on. I've really really appreciated that over the years. The Rust project has benefited immensely from your presence, and it definitely would not be in the state it's in today without you.