Yeah my personal experience is that if a SSE server has clients subscribed, and it goes down, the clients reconnect automatically once the server starts back up.
Only thing is the message ids reset when this happens.
I think this depends on the client/implementation. SSE call is just a http request with a continuous body stream. If it gets terminated clients could try to make another of those requests or not. That said the EventSource client in Browsers - which most people are likely using- will automatically reconnect
The SSE spec contains the `retry` and `Last-Event-ID` mechanism. Of course if you are making your own implementation, nothing is provided, but I'm saying that the spec has such mechanisms built-in.