The Big Bang Theory will bring new viewers with its cliff hanger because, at the very least, people who stopped watching will want to see what happens. BBT's loyal fan base has a loud social media presence and it has brought me and my family back. We can't wait for the return.
Since the show is so old, they are primarily relying on older, established viewers. New storylines will just keep it fresh for the people that like to already watch it. It would be difficult for a new audience to adapt to the storylines, as some of the show relies on knowledge of the characters and scenarios in the past.
Big Bang Theory is a good show with an outstanding cast but it is in decline. Most television shows do not last as long as Big Bang Theory have and eventually viewers want something new. New story arcs tend to stray from the content that captured viewers in the first place so it is unlikely that they will help.
This show is for a select few. I know many people whom dislike the show and say it is stupid and I do not think new storylines would make someone whom does not like the show watch it. On the otherhand people who watch the show would enjoy new storylines so they did not have to watch reruns.