Would be great if when the server crashes it would announce it in discord.

If the server crashes, mods can't do things anymore, so this is not possible.

Instead of printing server closed in discord, print - Server crash detected

Server crash is a bit hard to detect while the mod will no longer respond after the crash.
I have no idea how to do that without killing server performance.

Looks like discordintegration does this by checking both ServerStopping and ServerStopped events

https://github.com/Chikachi/DiscordIntegrationCore/blob/2ecff7707c733df9cf5f54c9f259cabbc0db5b72/src/main/java/chikachi/discord/core/Proxy.java#L74

Thank you, that is the one we use in 1.12.2