We all know about that but i'm emphasizing more on the number one citizen of the forum (head administrator), how will a new administrator emerge after Theymos? please understand my point.
It's probably up to theymos. The choice is probably one who theymos thinks is trustworthy. Since such choice isn't based on personal indicators, then it's probably on one's track record here and perhaps some correspondence here and elsewhere.
But since there are currently 2 administrators, if theymos leaves, Cyrus will certainly take over. But if Cyrus leaves before theymos, then theymos will have to choose somebody else before he leaves. Most likely, since he has already chosen his moderators and staff, then it might be just one of them.