It’s not a hypothetical actually. Many non-Semitic languages have adopted Semitic writing systems. e.g. Persian, Urdu, Yiddish. Sometimes they always write the

It’s not a hypothetical actually. Many non-Semitic languages have adopted Semitic writing systems. e.g. Persian, Urdu, Yiddish. Sometimes they always write the short vowels in, e.g. Urdu and Yiddish, but other times they don’t e.g. Persian. So it’s at least possible to write an Indo European language without vowels. Desirable? Probably not.