Should there be a power failure, you might lose recent data that is still buffered, but the file system structures, directories, inodes and such, will not be damaged. A shadow writing technique is used to ensure that structural changes are always committed automatically. The z/OS UNIX file system does its own repair, as needed, on each mount of a file system. This is based on records it keeps of changes in progress.

There is no fsck command and the z/OS UNIX file system was designed so that this is not needed. The fsck utility generally ensures structural integrity, not data integrity.

Of course, there is always a possibility that user data, critical file system data, or the media can be damaged, so prudent backup procedures are always warranted.