What happens if someone who has lupus catches aids? Is that a fatal combination?

Lupus and HIV AIDS. No, it's not fatal. Life itself is always fatal, as far as we know, except for hela cells. Having lupus and HIV infection together may shorten a person's life, but neither condition is rapidly fatal, nor is the combination. It depends on how severe the lupus is, to a degree, and how virile or rapidly mutating the HIV strain of virus is. But there are many known cases of people having both.