It's not at all clear that they would win. There is an article by a German lawyer on the topic[1]. The tl;dr of it is, that given that the car works mostly as intended and that any damage to individual customers is little (if it even exists) customers won't get back the full purchase price and probably not even any money, especially if VW were to provide a fix.
[1]: http://www.ferner-alsdorf.de/rechtsanwalt/zivilrecht/vertrag...