The open only fails if your process can't fork at all. As noted already, the return from close will give you the exit status of the child process. You may also get a SIGPIPE if you try to write to a pipe whose other end has gone away.

Update: See the section on Pipes in chapter 6 of the camel for more information; reading up on the specifics of pipes on your OS might also provide enlightenment (they are strange beasts, and can cause all sorts of oddball errors if handled improperly).