That's all but impossible to say here since the condition of the inside is unknown. Best thing to do when cutting into anything structural is support is as much as possible. Also of note, the rocker is in two parts. inside and Out, so just removing the outer rocker isn't necessarily going tp make you're car fold up.
your pictures show a LOT of scale. Might be worth cutting into it to see how thick what's left is. At some point, you will be in the same boat as me. My car (70 cuda vert) is as bad as yours and is scary as hell. However, it's a 70 cuda vert. so in MY head, worth saving. That's the hard choice you gonna need to make.
I was hoping to be able to keep the front rails in tact, but I've discovered that isn't happening. Go in and Go BIG if the car is important to you.