How much rust is repairable is different for different people.
I know a guy that had a turbo Firechicken that had some rust. He sold the original interior, intending to strip the engine and disc brake rear axle. Then he stopped at a restorer somewhere by Seattle and saw what he was restoring, which was in considerably poorer condition. I had to ask if he was going to repair the rust now and get another interior. Got a couple of expletives in return. He did strip it and scrap the body.
Same guy had a tree fall on a 1940 Olds Coupe. Looking at Olds production that year the coupes had a fair number built out of Olds production. When looked at against the General's total production, it was a fairly rare auto. It would have taken a fair bit of work to straighten the roof out, but with some metalworking skills it could have been saved. He cut the body up and took it for scrap. I have the frame. I got pissed with him over a few more things and refuse to talk to him.