Ah, good, and the Imperium doesn't give enough of a shit to raise an alarm if people randomly go missing, huh?
I wonder how many small scale disasters are running around that the Imperium just... Considers the Cost of Doing Business and isn't even aware of.
Its been what, 600 years since the imperium left?
From the looks of it, They went into some for of hibernation, and Sending Child and Man would have woken up more then the outlier's, Kicking off a feeding frenzy. AS is, from the side event it looks like a single one that had gorged itself... On like 10 ish People in a nineish month peroid. Given standard imperial Populations, If the False hydra's had eaten... lets say once a month during this "feeding frenzy" it might have eaten only a couple times a year when not starved, If that, Even if the Entire population was awake, Instead of some form of food coma/hibernation between meals, we could be looking at numbers as low as a few hundred a month, or even a year depending on the population of creatures.
For Imperials? That's CHUMP numbers, An Administrator wouldn't even have bothered to write that off.
Honestly? we are lucky in two ways. First, seemingly only one false hydra woke up from its hybernation that they went into to survive the loss of food, And second that it decided to gorge itself after being starved.
The false Hydra's Form of Gorging was like 10 souls before we killed it, If The false hydra Hadn't been gorging itself and was just picking off stragglers in a way that can be waived off easier, the colony might not have even gotten a clue when the rest woke up in a feeding frenzy.