That said, it honestly seems like they didn't know or care. No one told any of the subs she helped moderate (not even one of the largest on the site) that Victoria had been let go. If they had any idea what she did at all, and had any interest whatsoever in keeping the community together, they would have at least tried to get that information to the people who would be affected. Instead, they shoved her out the door and called it done until a celebrity showed up at their door with an appointment and no one knew what to do.
Anyone taking over her role should have immediately checked to see what was happening. Even if she left no notes or schedule whatsoever, they could have checked the AMA schedule, talked to the mods, and gotten some kind of temporary plan in place. Instead, they just let the whole thing collapse and then tried to sweep it under the rug later. It wasn't that they didn't know what she did, it's that they didn't care and didn't think it needed doing.
I've observed situations where people had to be let go immediately (e.g. deceitful resume) even though they were in some pretty critical positions that set us back after losing them.
There could have been a reason for the suddenness.
If your managers can't tell what you do all day when they merely need to go to reddit.com/r/IamA and see dozens of upvoted posts from celebrities whose top comment says, "Victoria is here helping me...", then I don't think you can really blame her for that.
A skilled executive makes sure they have a pulse on what's going on inside their organization beyond what they're told. Relatively few executives are that skilled.
That said, they fired Victoria and didn't replace her with anyone. That tells me that they both didn't know what she did in her role, and also didn't care. Anyone assuming the role, even temporarily, even without any of her notes/schedule/documentation, could have just checked the AMA schedule to find out that an AMA was scheduled, and contacted the mods to see what the arrangement was. No one did.
This isn't your boss not knowing what your code does because you didn't tell him. This is your boss firing the IT guy and not telling anyone until someone's laptop needs fixing before a big meeting and there's no one who knows how to do it.
I expect my boss to know that some people engage in dubious ethical practices to advance their own careers.
After all, if it were my job to do my boss's job, couldn't my boss be my boss's boss instead?
And you should be fired first from your managerial post if you fire someone yet not know what kind of work they do and what they are responsible for. For that matter you should be blacklisted from holding any managerial position moving forward.
Even if Victoria hid everything she did and didn't document anything, the tone of the initial response was one of surprise that seems to indicate they didn't fundamentally understand how everything worked.
If their first impulse is to fire you if they think you're not really doing anything, then they're not doing their jobs.
EDIT: And this is part of the reason why I prefer to live somewhere with tolerable worker protections. E.g. in large parts of Europe it would be illegal to fire someone in this hypothetical situation without going through a proper process of issuing warnings and consulting with the employee to ensure the facts of the situation are on the table.
EDIT: The downvotes seem to indicate I wasn't clear. I'm not saying the Reddit management team thought Victoria wasn't doing any work. However, it was clear that Victoria was spending time doing things that management didn't know about. From the sound of it, Victoria saw work that needed to be done and did it. Her job responsibilities likely continued to expanded as IAMA grew. However if management truly didn't know how involved she was in that, that is a failing of both management for not staying involved in the process and her for not communicating up the extra work she was doing.