I think it is much more likely that we will have a small number of lingua francas (right now English, Spanish and Mandarin are the top three spoken languages and serve as the lingua franca in various locations) but a plethora of local languages will remain.
Many African countries, but also Latin America, the US and Canada are examples of that. South Africa is a stark example with 11 official languages. Many South Africans grow up bilingual. English is the lingua franca there, but neither Xhosa, Zulu, nor Afrikaans will die out any time soon.
Language forms reality and vice versa. It always adapts to the needs of the speakers. Just look at English used be lawyers vs engineers. Geography is not the only factor for diverging languages. Social differences are also a factor, e.g, sociolects are specific to a socioeconomic class.
So unless human societies become a lot more homogenous, I don't see a single language emerging.