(3.34) Plot Rotation When a player's plot deck is empty, that player's used plot cards move from his or her used pile to his or her plot deck as a passive game effect of resolving the revealed plot.

What happens if I reveal Betrayal at the Wall (KR F79) as my final plot card, and its "when revealed" effect attempts to resolve when I do not have a plot deck?

You are not able to choose and reveal a new plot card, so the "when revealed" effect fails to resolve.

Combining these, it seems that if Counterplot is played on the last plot of a player causes that player to have all of their plots in their used pile (since plot rotation depends on resolving the plot), which means not having a revealed plot for the rest of the game (since the player will be unable to select a plot from an empty plot deck).

Hm. I would interpret "as a passive game effect of resolving the revealed plot" from FAQ 3.34 as meaning "as a passive effect during the FAW in which plots are chosen and revealed". I wouldn't interpret it as being dependent on the succesful resolution of any plot effects. As such, if you play Counterplot on your opponent's last plot, he moves the just revealed plot to the used pile as mandated by Counterplot. Since he doesn't have a plot deck during step 2, he can't choose a new plot, so the previously revealed plot remains revealed. The used pile moves to your plot deck in step 5, as usual.

I mean, if the moving of the used pile to the plot deck was dependent on the revealed plot "resolving", what do you do when you flip a plot with a constant effect as your last plot? It doesn't "resolve", because there is nothing to resolve - does that mean we all played the game wrong, and you have to play with a permanently empty plot deck for the rest of the game if your last plot had a constant effect?

I would just put down FAQ 3.34 as a case of the imprecise wording the FAQ is full of and famous for, along with passive effects that "trigger" and many other examples, and go with the sensible interpretation.

Besides, even if it is like you say, it wouldn't mean "not having a revealed plot for the rest of the game", it would mean you'd be stuck with the previously revealed plot for the rest of the game, no?

Rat is correct. The currently revealed plot doesn't go to the used pile until a new plot is successfully revealed. So Counterplots leaves the plot from last round as your current plot until the replacement is revealed. If you counter the reveal of plot #7, that leaves the plot #6 as the current plot (since there is nothing in the plot deck to reveal from as part of Counterplot's resolution).

And yes, the used plot pile still recycles. "After resolution" doesn't require successful resolution; only for the resolution step (Step 3) to pass - which still happens. It's like those effects that say "after defenders are declared..." still working because the framework event has passed, even if the defender chooses to declare 0 defenders.

Thanks for the clarification.

Are both the quotes from the FAQ?

So I definitely cannot reveal a new plot card if my 8th and last plot card is Betrayal at the Wall?

Correct.

Does that mean that the 6th plot would stay up and the 7th plot would be moved with the other 5 back to the unused pile passively in round 7 (Seems to be the case, just making sure)? If so, that would be a hell of a way to pin an opponent's Valar if they played it in round 6 and also stick them with a 2 gold, 0 claim plot for round 7...

Does that mean that the 6th plot would stay up and the 7th plot would be moved with the other 5 back to the unused pile passively in round 7 (Seems to be the case, just making sure)?

Yes. That is exactly what happens.