While I agree that Stone's reveal that he was the one to invite the Wolves through the Fortress Wall should not have been enough to knock Alaric so far off-kilter, I think there would still have been a good opportunity to lean in to one of the Dark Age's ongoing after-effects: the lack of clear lines of communication.
To put it another way: even if the Wolf Watch was as sophisticated as certain rival intelligence agencies across the Inner Sphere (which, it would appear, it is not), it makes sense for the intel the Wolf Empire does possess to be focused on its nearest neighbours, with little known about what forces are in place on the "far side" of Terra.
The Republic, on the other hand, has had much more time and opportunity to gather intel from across the Inner Sphere, not least on the looming threats heading their way from the Capellan Confederation and the Draconis Combine.
So, while Alaric would have walked into his final chat with Stone retaining a sense of triumph in the wake of his own conquest of Terra (as reflected by his overconfident goading of the Hell's Horses in the previous chapter), Stone could have shaken him out of his complacency by pointing out how many CCAF regiments are now within one jump of Terra - and how many DCMS regiments are expected to be so by the time the Fortress stops working.
And that, on top of all of this, imagine if those months he thought he had with the Wall staying up turned out to be more like like weeks...
(This would all still be Stone actually trying to "help" Alaric. It wouldn't do for Stone to lose his "investment" so soon, after all.)
Although, even if Stone himself wasn't planning on it, imagine if Tucker Harwell decided to send Alaric a parting gift of his own, by arranging for a recording of Stone's final moments to be broadcast in time for Alaric's coronation ceremony. I wonder how the new First Lord of the Star League might react then...