So when Undead Amos says to Holden "You know those things that killed the protomolecule makers? They're going to kill all of us" (meaning all humans everywhere) and Holden replies something to the effect of "Yeah, I kind of figured that."

What? Did you think 2 minutes later the entire human race was wiped out?Like a literary version of Sopranos cut to black silence?

First and foremost, apart from the bigger plot, not going deeper into the (call it what you want) "Zombie/Undead/Ghola (homage to Dune)"that Amos has become and how he/it knows what he/it knows is like leaving money on the table.

Second, Elvi is obviously honing in on what the beings are that killed the Proto-Masters and has already focused on the fact that what killed them did not kill us. More money left on the table.

In the end, I can see the resolution being that humanity's inability to conquer our own inherent divisiveness leads to our ultimate downfall. That's fine, but the how is left open as are all major characters' arcs.

Ending the series at this point on a 'cut to black' without resolution (hint: There was resolution in The Sopranos) is an epic fail literaily.

/rant off