But they didn't tell anyone this plan until way too late, so it failed. It's not even clear that they came up with that until the site was deep into the protests.

they didnt communicate the back up plan to anyone that would have needed it. In fact details of the backup plan only surfaced some 12-24 hours after the sacking and the subreddits going dark. SO whether there was a backup plan in place prior to this occurring is difficult to say for certain, that they have one now is not in dispute.

If you read the modmail leak from elsewhere in this thread it didn't satisfy mods who were trying to pick up the pieces either

Nothing short of an immediate team of people to replace her, and an entire site revamp to address their issues was going to calm any of their rage.

One person in, one person out?

As long as her replacement was engaged this whole mess probably wouldn't have happened.

Ok, but that doesn't answer all of the communication points. They had an email set up (despite being a communication platform, but if that's how they needed it, ok) and then they didn't tell the mods what that meant. Are they each supposed to send a question about everything they thought Victoria was going to be doing over the next month to that email?

Sure? Questions go there, then the person will follow up with whatever human replies and act appropriately. People leave companies all of the time unexpectedly, the world ending drama made it hard for most people to take seriously. Any immediate issues could have been handled with some speedbumps, if the mods were willing to act reasonable and proceed forward.