Jeff,
I don't think a car is ever completely beyond saving, even if you can only use the original materials for a pattern. At the Sumpter Valley and with the WRPS we have often been accused of taking on projects that aren't worth it because the car, locomotive, or structure are too far gone. Four Westside flats were saved even when several experts weighed in that there was no point in saving them as one already existed in California, locomotives don't get much more stripped than the number 19 and 20, our 1884 vintage coach was in two pieces with no interior, caboose three had almost no iron and had been on the ground since 1945! Hell, the coffin tankcar was rust and rot before Mike and the boys got their hands on it, and it's now probably one of the most accurate restorations of a wood car there is.
In the short of it, condition is not the issue when it comes to restoring these artifacts, imagination and determination are! Everything can be fixed if you have the right people involved.
Taylor