I think Wyatt's right. The flag only touches the other parts along its edge - if the other parts are coming out, the flag isn't going to do anything to stop them.
If you look at the lock cylinder, fork, and fork spring, they all appear to be interlocked together and with the frame so that their accidental removal would not be very probable. That, plus the fact that the hammer interferes with their removal, makes it seem likely that removal of the flag only is an acceptable way to disable the lock. Keep in mind that the lock cylinder and fork have to be properly aligned, or they will come apart easily. I wonder how many of the "parts falling out" examples have been caused by this.
Still, if as Justin Wilson called it, you are a "safety man" (wears both belt and suspenders), take all the parts out. Your choice.
Buck