Yeah thats pretty bad rot.
You'd need to remake the inner rocker/floor, the support (center piece that joins to the pinch weld) and outer rocker.
And thats only the areas you can see right now. Where is else is there corrosion that isn't too far behind that? Or not rotted through yet. It would be a good learning experience for rust repair though
but thats a big patch job.
Even looks like your door seam is nearly ready to bust open
