Do these really ever result in access failures instead of just hangs? How are they surfaced to processes?
In my experience, all these things just cause whatever process is memory mapping to freeze up horribly and make me regret ever using a network file system or external hard drive.
Most I/O calls return errors when reads or writes fail, but NFS, for example, would traditionally block on network errors by default — you probably don't want your entire lab full of diskless workstations to kernel panic every time there's a transient network glitch.
You also have the issue of multiple levels of caching and when and how to report delayed errors to programs that don't explicitly use mechanisms like fsync.
In my experience, all these things just cause whatever process is memory mapping to freeze up horribly and make me regret ever using a network file system or external hard drive.