They’ll have to get a new SAS controller unless the RAID controller has an HBA mode. Running ZFS under a RAID controller is the best way to lose all of your data.
ZFS is wonderful but it takes quite a bit of planning and specialized knowledge to implement properly. Your fear of a failed RAID controller is a bit much, too. I’ve had to deal with a single controller failure in 30 years of IT (and I’ve done warranty work for all of the major OEMs in corporate IT for most of those 30 years)
It is the only approved method for data destruction for the several banks and government agencies I support. If they trust it, I trust it.
I have checked a couple of times out of curiosity, after a secure erase the drive is as clean as if it had been DBANed. Sometimes things are standards because they work properly.