I don’t think the effect of the bombing of railroads would have been as trivial as you make it out to be, especially since the bombing of Germany was incessant and could be repeated at will. In addition, steel was precious to Germany and their industrial infrastructure was being smashed, so even repairs would have been seriously problematic.
As for Churchill, what I read was that much of the death camp information was confirmed through coded messages decrypted by ENIGMA. So if they acted on it, the fear was Germany would respond by shifting to another code system entirely. Not letting on that ENIGMA existed through Allied actions was huge part of using it effectively.
That’s interesting about Enigma, a very similar story to Magic.
Rail lines weren’t all that tough to repair. Bomb craters got filled with gravel. Damaged rail was heated and straightened or rail borrowed from a less traveled line. And if the Germans had decided not to repair the rails the inmates would simply have starved and new arrivals made to walk any breaks in the line.
When the Germans learned that we would make repeated strikes at a target they would move flak 88 guns in to greet the bombers. I’m sure they would have done the same around the camps. You might surprise them once but not many times afterwards.