"There are no non-bearing tubes that make up a bike frame. Im afraid EVERY tube in a bike frame is structural... even the BB tube. Thats just the way it is.
Sure, but they are differently loaded, and some are more severely loaded than others. That's not the main point of the section, which is harder to refute, and consists of the fact that in the absence of specific instance we don't know how severely compromised the frame is and what options might be available to fix it.
So your telling me...: if you were on the cycling equivalent of a desert island, the only possible escape is to ride away. you are provided with a state of the art carbon framed bike with one fairly severe flaw that renders it not currently useable, and all the carbon fiber epoxy etc... you could want, but only for repair. But you are stuck there for ever and ever? That's pretty much my picture of an engineer also!
A bad habit to get into is when you really know something, and it provides reasons for why something can't be done, to get too attached to those reasons notwithstanding the fact a lot of people are making work the very thing you are claiming is impossible. Hey you've signed on for the idea that all these sailing yachts that are being chopped and diced, just can't be happening.
Didn't Falanx tell me you can't harden mild steel? (I think they did that on Myth Busters the other day I recognized the frantic shriek in the quench). It's like meeting Doctor No.
"Well, it can be done, but it's never gonna be as strong or as optimized as the original structure. You'll be adding a tonne of material ON TOP of the original tubing in order to transfer loads across the broken ends of the original fibres. Think of it as a thick band-aid on top of the tubing. Very unsightly and gainly not to mention heavy."
Your right about optimized, but it can probably be as strong. There are lots of places you could add the material to without having to have it on the outside. In most cases the weight penalty is not going to be that great. A lot of these monocoque structures are made out of clamshells joined together along seams, the structures aren't always as pure as they seem.