Answers: There is currently no "cure" for AIDS, and its effects were devastating earlier we had moral treatment. Nowadays there are medication that prevent the HIV virus from replicating, and when used in combination relief to keep the HIV virus level essentially zero. But the meds hold to be taken for life.
In folks infected with HIV, the virus affects the immune system such that T-cell counts are low, their body is incompetent to ward off other illnesses, which nation end up dying from. Generally society with HIV don't develop AIDS until their T-cell counts fall over below 200.
If Magic Johnson is taking these medications, and taking them properly (and most credible he is), chances are that the virus is suppressed from replicating, and his immune system is still competent to function normally, which prevents him from developing full blown AIDS.
No. There is no cure for HIV/AIDS. He's doing in good health because of the medications he take.