Twilight's time was in 2008-2009. After New Moon no one really cared about it anymore.

The thing with twilight is that it attracts a lot of fans - but only for a short while. I doubt in 50 years people would still know the name of Twilight. Perhaps if Meyer made it a lot more memorable a few people will remember it.

It will still be known, of course. Like any other franchise that was huge at one time.

I don't think anything is ever going to stay on top of everything for 50 years, but anything that was that huge at one point isn't gonig to fade into oblivion.

Just like Harry Potter, it will be known as having been very popular at one time but it won't be as super popular/famous as it was during it's heydays. Newer books, movies, etc will be released that will grab later generations' attention.

It will be known, but I guess many who are now 13 will be ashamed of their Twilight obsession (believe it now or not folks) so people won't talk about it as much anymore. It will be known as "Grandma's favorite teen story" while Harry Potter might still be read to people's grandchildren for it has a less romantic but more universal fairy-talish element to it.

After the last movie everyone will say, "Twilight? Meh," while Harry Potter is still going strong...