Is there a reason to take the forum down, other than low interest and activity? I can remember that when I joined LeftyBassist.com a few years back it was also a forum where every once in a while a couple of posts were made here and there, but over the years it got busier and busier.
I am also guilty of neglecting this forum but I like the idea of as much exposure online for lefty bassists. Another possibility would be to expand the site and open it up to guitarists or even all musicians in general to get it populated but retain the existing section for lefties. I think it's been very well done.