The piece in your first photo is the end part of the outer rocker panel. The inner rocker panel is further inboard and is mostly vertical. The inner & outer are spot-welded down the entire length and form a box section rail. If you are good with metal, you can fab a patch for this area. I had the same problem; just be sure to have good clean metal to weld onto. As far as structure is concerned, there are spot welds all over in this area; just be sure to duplicate them and use the same guage metal. The piece in your last photo that spans the rocker & frame rail is available as a repro, I've seen them out there, just can't think of what they are called; hope that helps!