Frankly I doubt you would break the frame at the dent. As odd as it sounds it's in a relatively low stress area and steel is pretty forgiving. I see the real issue being alignment. The chance that the frame is still in alignment is small. That dent of the stay no doubt pushed the stay toward the center of the bike and in effect shortened it which in turn will make the wheel not centered between the c-stays - which will then make the bike pull to the side.

If it were free and you wanted to goof around with it then that would be one thing - to part with money for it is another all together.

Best of luck to you.

Dave