In the US, at least, most commercial sausages are made with artificial casings, rather than gut casings. I'd be surprised if that wasn't also the case in France as it makes industrial-scale production a lot easier without much difference in end product.

Despite their efforts, dictionary definitions aren't always in sync with common usage, and it seems obvious that the latter is what we should regulate on.

The dictionary describes the way words are used by people; it doesn't prescribe the way words must be used. If the way people use a word changes (e.g. if people start using the word "sausage" to also refer to these vegan products), the dictionary changes. You don't change the law to match the dictionary