George,
"Detached" doesn't tell us about the nature of the failure, so it's kinda hard to bless or condemn the extension itself.
A metallic extension as you describe was probably an attempt to reduce temperature at the interface with the nylon tubing. In itself, that is not a crazy idea. Most nylaflow tubing grades are rated at a max operating temperature of 150 to 200F (melt is 365 to 500F). The 1000 psi pressure rating often quoted (by Aircraft Spruce, for example) is at 73F.
Returning to extensions, God is in the details...materials, fabrication, etc.
Side note; standard nitrile caliper o-rings fail if caliper temperature is pushed above 250 or so. The usual prophylactic is a switch to viton o-rings, good for a bit more than 400F. My point here is that if the fitting was de-soldered, the calipers need to be rebuilt, as the o-rings will have been toasted.
Now I branch into opinion. If as an auto dealer, I installed nylaflow plastic brake lines and compression fittings on your pickup truck, I'd be branded as a criminal idiot. I do not understand why builders continue to install them on fast aircraft. Personally I think you have a fine opportunity to install something suitable.