Yes, I also had a "1 disk failed, second disk failed during rebuild" event (like the parent, not your story) with mdadm & RAID 6 with no issues.
People seem to love ZFS but I had no issues running mdadm. I'm now running a ZFS pool and so far it's been more work (and things to learn), requires a lot more RAM, and the benefits are... escaping me.
Are you sure the data survived? ZFS is sure and proves it with checksums over metadata and data.
I don't know madm well enough to know if it does this too.
People seem to love ZFS but I had no issues running mdadm. I'm now running a ZFS pool and so far it's been more work (and things to learn), requires a lot more RAM, and the benefits are... escaping me.