Wow! Another 10+ years on... social media didn't do anything to fix itself, and fans are still waiting for The Doors of Stone...
Attacks on authors is not a new phenomenon at all. In the Coda at the end of The Song of Susannah (Dark Tower book 6) from 2004, Stephen King writes about exactly this, including the letter that someone was dying of cancer. In fact, I'm sure that is were Rothfuss got the idea.
And aren't GRRM's fans waiting just as long too. The only difference here, is that if you believe Wikipedia then in July 2020, Rothfuss's editor and publisher, Betsy Wollheim, got just as annoyed as some of his fans.
There are many very good reasons to leave X/Twitter and Facebook and social media completely, but social media certainly doesn't cause this, it just make it much easier to contact the authors, poisoned internet rather than by poison pen.
Having a good rant and a vent must have made him feel much better at the time but the problem of social media is that the evidence never goes away. It wasn't the best idea to have. He shouldn't have ignored the death threats though, you must take those seriously.