Keeping the pool writable while there is a missing disk will introduce data corruption for duplicated files. I can't add an option (even an advanced option) that corrupts data.
Simple example:
- Pool part gets disconnected (whoops).
- Duplicated files continue to get read / written to on the pool.
- Dropped off pool part gets reconnected.
- Any duplicated files on the dropped off pool part that were updated while it was disconnected are now corrupt (due to their contents being different).