I'm sorry about your rooster.
Without testing, we have no way of knowing what he had.
How long had you had him? Was he new to your flock?
All respiratory diseases are contagious, so if he was with your flock, then they were exposed. The best thing you can do is observe your flock(s) for any symptoms that may appear.
Treating prophylactically is not practical since you don't know what to treat for.
There is no "cures" for respiratory diseases, just treatment/supportive care for
Symptoms.
Symptoms of respiratory disease like MG is usually treated with Tylosin, while symptoms of Infectious Coryza are treated with Sulfa antibiotics.
Here's good information about some common poultry diseases
https://edis.ifas.ufl.edu/publication/ps044
IF You have any birds show symptoms of respiratory disease, then getting testing through your state lab or through an independent lab like Zoologix would be a good idea, this way you know what you are dealing with and know how to proceed with treating symptoms.