As I am French and happen to know some stuff about the series, I'm gonna answer the questions below. First, Virginie Desarnauts really appeared in Les vacances de l'amour (ep 25&34, s4) as in Le miracle de l'amour (ep 15, 1st season). You can find those informations on her IMDb page. Second, I'm gonna reveal what happens to Hélène at the end of Le Miracle de l'amour : Episode 84 : Hélène learns that her grandma, who's living in Australia, is suffering from a bad illness. So, she decides to go there and take care of her. Nicolas goes with her. And that's it, no other explanation. She comes back in the fourth season of Les vacances de l'amour.
Also, the series is available on DVD, in France anyway.
Also, the series is available on DVD, in France anyway.