Take some sand paper to the rusty parts. You may not have to work long before you get to shiny metal with only a few specs of rust. Take a picture and show us. Then use some rust converter over all (including inside the steerer).
Then put the steerer in a vise and start yanking on the blades every which way. Then put the fork back in the frame, attach a wheel and start banging the front end around--see what happens. I predict that it is rideable.