Room are persistent by default when there is a non temporary working dir.

server/lib/prosody/config.ts

@@ -134,6 +134,8 @@ async function getProsodyConfig (options: RegisterServerOptions): Promise<Prosod
   if (paths.permanent) {
     // TODO: add a settings so that admin can choose? (on/off and duration)
     config.useMam('1w') // Remove archived messages after 1 week
+    // TODO: add a settings to choose?
+    config.useDefaultPersistent()
   }
   let logLevel: ProsodyLogLevel | undefined
   if (logger.level && (typeof logger.level === 'string')) {

server/lib/prosody/config/content.ts

@@ -230,6 +230,14 @@ class ProsodyConfigContent {
     this.muc.add('modules_enabled', 'muc_moderation')
   }
 
+  /**
+   * Rooms will be persistent by default (they will not be deleted if no participant).
+   * Should not be used when using a temporary dir.
+   */
+  useDefaultPersistent (): void {
+    this.muc.set('muc_room_default_persistent', true)
+  }
+
   setLog (level: ProsodyLogLevel, syslog?: ProsodyLogLevel[]): void {
     let log = ''
     log += 'log = {\n'