Depends on what they do with the site, I've seen big file share sites with millions of users lose all their users to a rival in less than a week after one update. Everyone thought that particular file sharing site was the best, and they died in under 7 days. It was amazing to watch, it was called morpheus. Same thing happened to friends reunited (facebook replaced that)
Hopefully it does die out, as the replacements are ALWAYS better.