Yeah, that pic shows the cancer all the way up to and into the toe board and the frame rail. Take out the floor pan and see what you have left to save. While you are in there, you may want to consider replacing the toe board as well. Or, if you have welding skills, at least a patch to put new metal in there. Good luck with it. If you are rich enough to own a plasma cutter, then the job will be easy. If not, then you can at least rent one. I would do that before drilling out all those rusty spot welds.