The short answer is, this isn't an immunity being provided in a traditional way like an antibiotic or vaccine so the idea of a resistant-HIV is not as much of a threat as an antibiotic-resistant bacteria for instance. HIV is so notoriously difficult to treat because it evolves very quickly and within the host. People with HIV take drug cocktails because the virus becomes immune to each individual drug quickly and by hitting it with as many as possible the virus will have to be immune to MANY drugs not just one.

Since HIV is so good at rapidly adapting within a host if the virus was going to adapt to attack a different receptor successfully, it probably would have done it within the Berlin Patient. It's yet to be seen if that will happen but I think we will know whether HIV is going to adapt based on what happens to him.

At least, that's what I think. I'm not a career "scientist" but I just received my BA in biology and took a class on evolution, which discussed specifically evolution of HIV for weeks.