Only going to offer my advice as I really don't care for comic books or super hero moves as fanatical as someone like Alex
Feel what you need to do is best for you, first. Yeah it'll suck to see the board close but if it's a chore for you and no longer as fun as it once was you should focus on where your real interest are. Whether that means stepping down or closing the board I don't know because it seems like there is someone that would step up as the comic books have a pretty large fanbase but on this site I don't know if that's the case. While comic books and super hero stuff is a large medium it being X-Files limits it quite a lot and has the possibility of having less range of conversation.
Stay happy
