My chainstays have been eaten by rust, can something be done? I hope you are all safe and sound and your Christmas time is at least decent in these pandemic times.
The other day I decided to give a good clean to my steel city bicycle and I removed the stand, which was quite tightly closed on the frame. Doing this I discovered two horrible holes in the ground-facing side of them:

(I did not notice the ride quality as being very soft, but my other bike is an aluminium bike with a carbon fork, so probably I am biased towards stiffer bicycles)
The other side is in good condition, no rust inside or outside.
Now, is anything possible to fix them? I would like to get 2/3 years more of life from this frame ... in its current form, without building it as a frankenbikes or other funny contraptions :D , if possible.
The only thing that can be done to save the frame is to have patches welded over the holes. You would need the expertise of a professional welder to get it done properly so that the frame is made structurally sound.
Unfortunately, you may find that this repair is more expensive than simply finding a similar replacement bike or frame. The welding repair job will involve removing the wheel, crank, bottom bracket bearings and other components to in the area to be welded. The frame will need to be repainted as well of course.