On the TB20, it "cannot" happen because there is a shaft that joins the two together.
Until the shaft breaks! Do not believe ANY statement that it cannot happen! All you need is corrosion in the right place and then the extra strain from another failure and the impossible happens!
C172 certainly WILL fly with Flap 40, the big problem with Cessna Flap 40 is the push needed on a GA, but once you have the trim sorted it is quite flyable.