Yeah, Tumblr is so... ephemeral. It's frustrating. I remember returning to the Trigun fandom in 2011 (when most people had left) and falling in love all over again with the early-2000s meta and conversations that had been archived on LJ. One thing I appreciate about AO3 is how the comment space has been designed to take after LJ, to encourage the back-and-forth that I saw so often when I was just first starting out in the fandom. (It's a real joy when I see people using the space for that purpose.)