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)