I am sorry to hear you are worried about Richau. My name is Rebecca. I am a veterinarian and will do my best to help.
There is a surgical procedure, of placing a stent to hold the trachea open, that is done by some speciality hospitals and universities. Your local vet may be able to refer you to a place that can do this.
If this were my own 12 year old dog, I would first try medical management. A collapsing trachea causes a "vicious cycle": the trachea collapses, making the dog cough. The coughing causes inflammation in the airways, causing more coughing, causing more inflammation, etc. Often a secondary infection will form as this progresses, making the cough and the condition even worse.
If this were my own dog, I would continue the drugs he is taking, but would add a course of antibiotics and most importantly a good cough suppressant. You have to control the coughing to stop the vicious cycle. Neither of the medications he is taking now are cough suppressants.
The best would be hydrocodone, if you can get it from your veterinarian. The goal is to give enough hydrocodone to get the cough controlled, without giving so much that he gets drowsy. Over time, you can gradually reduce the hydrocodone and antibiotics, and maintain him on the Dermipred for inflammation and the hydrocodone for coughing.
If he were mine I would try this and if this does not help, then I would consider surgery. At 12 years of age, there is some risk with anesthesia and surgery, so I always try medical management first.
Let me know what other questions I can help you with. Rebecca