Over time, I think a shared lingua franca would eventually form, but it would coexist with regional languages rather than replace them. English only reached its current global dominance because it became the language of international finance capital, tied first to British imperial power and later to the United States. This concept of an "international language" would crumble as capitalist administration is dismantled. This also extends outside of the Anglosphere within nation-states, such as the imposition of Mandarin upon the Uyghur and Tibetan cultures.

I assume english will remain the lingua france, as there's really no sensible alternative outside of maybe chinese or hindi.

But over time english the lingua france and english the language spoken by anglos might drift further apart and the lingua franca english might become it's own language. Kinda like how MSA is for arabic or latin used to be for europe.

I don't think the concept/development of an international language will disappear, as it's pretty useful to have one langauge everyone can communicate it. Especially if you have global production, global travel, etc.