I'm inactive today; that does not mean I will remain inactive forever. If the board in question was lacking moderators to handle the board, then the admin could have appointed others, but in this case there are still two who are very active, just as you have noted.
To Theymos: if you didn't noticed, I present it to you today.
The admin oversees everything, and because the said moderator is not active today doesn't mean he or she won't be tomorrow. People have lives outside this forum. Unless there is some sort of danger attached to his account for suspected hacking or anything of that sort, I don't see a reason to denounce the person from his position… that's just my 2 cents.