I'm curious about the "daily backups". Does this mean that if the data is deleted from the Apple Keychain the app has a local copy that can be reverted to?
Anyway the Apple Keychain retain a local copy on the device, which means that even if in airplane mode Obsidian works by reading the local keychain.
Obviously if the whole keychain gets corrupted/wiped then there is no way to recover, but I find it unlikely, or at least never heard about it.