For an admin to be removed from their position, Spock has to remove them himself. there is no "heirarchy" of admins, so one of us isn't higher or lower than any of the others.
For someone to become an admin, there needs to be agreement within the admins that another one is needed, we talk to spock about it, and then we go about finding that admin. There is no set way to do it, there have been multiple ways its been done in the past...when RCK became an admin, it was a vote from the committee and admin teams that chose him over others (correct me if I'm wrong there RCK, I'm pretty sure thats what we did). When DWill and I became admins, we were chosen by BOB, who was given permission by Spock to choose people...he chose us because he was being deployed, and he needed people to take over his duties on the WB and in Chat, and at that time, we were seen as the best candidates. When Blade was chosen to be reinstated as an admin, we had told spock we needed someone to help us out, and he let us decide who, and the admins at the time nominated and voted for Blade.
To remain an admin, you don't quit, you do your job, you don't screw up. You screw up, you can be removed if the other admins and Spock agree that's the right course of action. I myself have quit and then been reinstated. That was because when I quit, I had quit because of all the hits that the community had given me for screwing up. I screwed up, I quit, a few other admins talked to me, and I came back. There was a time when BOB and I had been removed from our positions for playing before the game began. We were removed, then reinstated under probation for 3 months, and not allowed to play for over half of the round that this happened in.
Some admins get removed because of their inactivity. I had removed Siege from admin privileges soon after I had been appointed in that position because he hadn't been seen or heard from in a longer time then any of us could recall. That's more of cleaning up house then kicking someone out of an admin position though.
As for admins actively playing the game...I myself try to find time as best as I can, and it ends up being pretty sporadic (ask kiky about that one), but I do what I can. I know that others do the best that they can as well. At the same time, it sometimes help to not be actively involved in a round so that, should a problem arise, the issue can be resolved without having to worry about bias. That's not to say that we (the admins) should not have a character in game. All admins should have a character in game that they check as often as they check the message board (for me, that's every time I load my browser...I admit I don't check my game messages that often, especially up until the past couple days...midterms had seen to that).
If there are concerns regarding specific admins, feel free to message other admins about the problem. The issue will be resolved as best we can, and no names will be called out. So I wouldn't say, "So RCK, turns out Kiky thinks that you're a failure and shouldn't be admin." I would say "RCK, I've gotten a message from someone who is concerned about your ability to perform your Admin obligations as well as they need to be." (Disclaimer: This was made up on the spot, I've received no message of the sort...yet
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(This message was a lot more long-winded then I had intended...I hope it helped)