You need to close it and check for errors as part of the happy path. But it's great that in the error path (be that using an early return or throwing an exception), you can just forget about the file and you will never leak a file descriptor.

You may need to unlink the file in the error path, but that's best handled in the destructor of a class which encapsulates the whole "write to a temp file, rename into place, unlink on error" flow.