If the games have been shut down then yes, I wouldn't see why not. Dungeon Fighter Online was probably the only game (afaik) that would fall under this category, but it seems that it have been brought back again:
http://forums.d2jsp.org/topic.php?t=70769911&f=154I think the more games d2jsp support the better. Users should atleast have the option to discuss the game even tho there are only a few left that still plays the game. "It looks bad" is not a good enough argument for me, if you want a cleaner view you can "Toggle View All Subforums" at the bottom of the page.
In summary, if the game has actually been shut down then I don't see why not. If it's still up keep it.