I think that society is the interaction of people with one another. Social media has been a way that people can interact with one another. The downfall of one method of communication over another is more likely than the downfall of society.
Over the last hundred plus years, one form or another of social media has become popular and sometimes faded. Newspapers, cinema and television, letters, telegrams and telephone conversations, email, sms, instant messaging, voip and interactive web sites.
I do not know which future creations, or what combination of existing technology of today will be the most popular social media in the future, but I am confident that people will continue to communicate with other people in which ever way they think is the easiest or most enjoyable.
So, will social media lead to eventual downfall of society? No.