I'm not sure about "ride what you can replace" since I agree odds are pretty low that you'll destroy your entire bike/frame (it does definitely happen though), but "ride what you can damage" is definitely in order. If you go down even once, you'll scrape up your bars, or if you collide with someone going similar speed, scrape the paint on your frame even if it works fine. Bottom line, be willing to be ready for some minor damage or cosmetic damage at some point.