On the chance she has to step down because Kane succeeded... remember that Alessandra "jokes" that she might not have to worry about stepping down if something unfortunate were to happen to another member.
But the question remains: WHY would the 7th member be MIA?
With the Elena stepping down being a future plan and not a done deal, it does make me wonder about the conditions of her actually leaving. While Olivia's victory in the Gambit is still open ended, there's no scenario where she doesn't get a seat on the Board. With her parentage now public amongst KG and DS executives, there is no reason to not make her a Board Member at the Welcome Party, so why don't they? If they need a Board vote, they would have done it before they offered, and they have offered, which she has accepted (you don't offer someone a job, they accept, and then vote if you're going to hire them) so there's no need to wait.
I have wondered if Elena's "step down" is the punishment Yvette warned her about on the pier, which Elena of course did not heed, and since she's being fired anyways, might as well cheat a second time and tell Olivia who her mother is. It is the classic corporate spin: no executive is ever fired, they merely "retire" or "step down to spend more time with their family". Either that or Elena, as representative of Team Olivia, has been free to cheat without retribution.