The Ancient Vietnamese, which eventually, after adopting Chinese character and modifying them to fit the Vietnamese vocabulary became the “Nom” script.
However, Nom script become very outdated, especially when France invasion use the Latin base character. Vietnam adopt the Latin base character, and reword the Nom into modern Vietnamese writing system. The languages is still there, what change is the character types.
Most Vietnamese doesn’t learn Nom, there are course for those, but it’s really isn’t practical's anymore.