I'm not that familiar with truck brakes, but if brake fade does in fact represent a loss of friction, then it's not something that locomotive engineers deal with much. Modern rail equipment, both cars and locomotives (for the most part) uses HF Comp (HIgh Friction Composition) brake shoes that are designed for high heat applications. HF Comps actually have better friction/adhesion quality at higher temperatures (above ambient) and engineers have to accommodate the extra time needed for the shoes to warm up when they make an initial brake application. If you wait until your 12,000 ton train is already cresting the top of a heavy grade at speed before applying the brakes, you will at best be speeding before the brakes warm up. At the worst, your speed will have become excessive and you have a runaway. There are many other variations on what can happen in between to recover or fail, but like another poster said above, engineers must be qualified on their territory and plan their actions accordingly.
The only thing similar to the described fading would be on a very long grade where already thin shoes are worn thinner and their ability to take the heat diminishes to the point that they basically self-destruct and are no longer functional or in a true emergency situation where control of the train has been lost and the wheels/shoes have become so hot that they have actually begun to melt. This has happened to varying degrees in runaways over the years. See Cajon Pass runaway reports for details.
The issue of fading in dynamics isn't related to friction, but is a concern depending on equipment and speed. Older flat type dynamics had a limited effective range, quickly becoming worthless below 20MPH. Newer DC locomotives had Extended Range dynamics that considerably lowered the lower end of the effective speed range(6-7 MPH), but it's still a curve that flattens to 'almost useless' at lower speed ranges, requiring the engineer to transition to independent brakes to actually stop the train. Newer AC locomotives are capable of dynamic braking virtually to a stop. The dynamic brake effort curve also tapers off at higher speeds with DC (generally above 25 MPH), but less so than at lower speeds. The newest DC locomotives have even higher capacity dynamics than the older ER types, too. It all depends on what you're operating.
What the #*** did we just hit, Over ???