People create languages to communicate on an as-needed basis. And languages that aren't needed anymore or that are supplanted by other forces fall away.
Language is not a finite resource. Language is not equivalent to culture, and even if it were, culture is not a finite resource.
I'll be thrilled if every language in the world disappears except for one, and we all communicate in it. I don't care which one, although ideally it'll be a simple or logical one, like Indonesian/Malay, with a writing system like Hangul.
I wouldn't even be bothered if it's my own culture disappearing if the upshot is the global efficiency gain of everybody speaking, reading, and writing in ways that everybody else instantly understands, without the need for multi-lingual versions or translation software or human translators.
People who want to still do learn latin or Ancient Greek or Sanskrit. And even if they couldn't, the trade-off is still worth it times a thousand.
What about the mental exercise and developmental benefits of being bilingual? As a multi-lingual person myself, I recognize this. But there's no reason your other languages have to be from a particular culture or can't be constructed languages.
I'm guessing bilingual English/Korean kids or bilingual Spanish/Toki-Pona kids get all the same benefits, regardless of the particular language pair.