Now if I understand correctly, unless someone inherits a private key of his, his bitcoins are effectively dead now, right? I wonder how this will impact the economics of cryptocurrencies over time: I'm starting to see more and more reminders to congratulate dead people on work anniversaries on LinkedIn, and it feels quite morbid.
If he didn't have a backup plan in place to be accessible by his estate, then yes, the coins are dead. The coins dying with him are actually the best case scenario for all other holders. "Lost coins only make everyone else's coins worth slightly more. Think of it as a donation to everyone." - Satoshi Nakamoto
One of the disadvantages of crypto, I suppose, is that people could gang up and hard fork against any arbitrary billionaire even if they were alive.