^Sadly, I think this is true.
Female pop groups rarely stay together very long before ego and ambition breaks them up. It seems like they're only together long enough for each member to accomplish some level of fame before moving on. I bet with SNSD, the more popular members will continue singing with solo careers, the less popular members will become TV personalities, and the least popular members will just fade away.
Keeping this in mind, I've decided to not let it bug me and that I'll just enjoy them for what they are and for however long they're together. I doubt neither of my favourite members would continue with solo careers and I don't find any of the lead vocalists that interesting so SNSD is it for me.