Yea, they're just in memory, so they're lost. Erlang/Elixir doesn't solve this. There's no getting around the fact that you need an ack that your event was processed and saved to some durable store. A supervisor won't save you from lack of acknowledgment at the app level. Any restart or retry logic within beam itself is useless if a beaver chews through a power cord and the machine halts. And what is an ack, anyway? Is an ack from mongo as good as an ack from postgres? This is all stuff the language can't know. These are all business questions, all the language can do is give you tools handle these cases, which Erlang/Elixir does.