That’s what redundancy is for: Preserve data integrity even when the underlying media is not reliable.
But for ZFS to properly protect your data, you should still react to hardware failures and act timely—which you have done. When ZFS errors occur, you have lost data.
You may use this resource to assess the condition of the failed drive:
But, essentially, if it has failed a long SMART test, the drive is due for RMA or for disposal.
