Having grown up with your house, Rick, I can identify with it's problems, both structural and cosmetic.
Have you considered adding a second bathroom to your house? Would your geographic location and neighborhood support such an improvement from a financial perspective? That would certainly make Mrs. Rick a lot happier during the reconstruction of the current bath and perhaps enhance the livability of the house in future?
OK, so that's a no. While it may be possible to do some repair work in the window area and increase the longevity of the current shower, it's unlikely you can match or even closely approximate the current tile surface. But done such repair where the contrasting result then becomes a "feature." Some customers can tolerate, or even embrace, such features, others not so much.
But I would caution that once you start trying to tear out that small area of the shower wall for repair work, you are very likely to find yourself in an in for a penny, in for a pound scenario.
You won't know how difficult or destructive removal of the tile surface might be until you give it a try. I've been told that sometimes the tile comes off rather easily. I've never encountered a shower of that era where that was the case, but I suppose it could happen.
Easiest fix? Put a curtain rod across that back wall and invite Mrs. Rick to pick a nice curtain to hang there semi-permanently. You can try to sell that as a feature, too, but............
My opinion; worth price charged.