Good, you are on the right track for understanding how random mutation and natural selection (rmns from here on) works.
I am quite familiar with population genetics and molecular evolution, but sure, yeah -- thanks for your laudatory comments I guess?
So consider the simpler case when HIV evolves very rapidly to single drug therapy. How do compute this probability?
We'd need to know population size, fitness of wildtype viruses compared to drug-resistant mutants, mutation rate, no. of copies of mutant phenotype in the population, etc., to estimate probability of fixation of the drug-resistant mutation.
But get to the point. You don't need to walk me through pop genetics.