That's where backups come in. Any filesystem can get corrupted. Though for ZFS it's less likely than with something like ext4. Even though both have journalling, only ZFS has copy on write.
My problem was rather with problematic updates of zfs itself.
The update "helpfully" updated initramfs for older kernels too... and if something broke, it broke previous versions too, so they all were unbootable. Eventually I ended up with an USB stick at hand with known bootable environment :(
