ZFS will throw an error upon reading data where it cannot repair it from checksums.
Discussion on “copies” here: The ZFS "copies" features is useless: Change my mind
I definitely wouldn’t rely on it on a single drive. Perhaps consider purchasing another for use in a mirror in an external 2-disk enclosure?
Then you’re also into the realm of long-term archival in general. If it was me I’d be thinking cl**d services such as AWS Glacier.