#but this guard stuff needs explanation that the predominant 'kidnapping' theory simply doesn't explain...

[eldritchtouched]

Weird Guard Behavior with Elphael/Haligtree/Malenia

So, in mysteries, there is a cliche about when "the dog doesn't bark."

The scenario in those stories is generally that something looks like a crime done by a stranger, but the guard dog didn't react to the presence of an unknown person. This is evidence in the story that the person was known to the dog and, thus, not a stranger.

Elden Ring has a similar thing going on with Malenia and the Haligtree, though a bit more complicated because the guard dog is a very simple thing. In cases where it's people instead of guard dogs, it's more a matter of, given what is established about the characters and/or factions, what would we expect given various details.

We have a general idea of their characterizations, and what the likely scenario is. So there's a few questions that are important to answer, to understand their behavior and work from that. First- do they know Miquella is gone? Second- what are they doing after they know that?

We have an answer to both.

Malenia knows Miquella is gone, as do the Haligtree soldiers. Malenia outright tells the player this information ("as I awaited his return") and her armor specifies that she was waiting for Miquella at the foot of the Haligtree. The quoted dialogue on her armor is specifically her consoling someone else and that Miquella "will keep his promise." The Haligtree soldier ashes, too, note that Miquella isn't there- that's why they're despairing.

A common idea in the fandom is that Malenia doesn't know Miquella is gone at all. Likewise, I've seen routine complains that the player cannot encounter Mohg before Malenia, then go to Malenia to tell her about Mohg and Miquella and getting her help to return Miquella to the Haligtree. This actively ignores that Malenia and the other people in the Haligtree all know Miquella is gone. (This taking off confuses me because Malenia outright tells the player that she's waiting for Miquella.)

We also know the other answer- what are they doing? They are waiting for him to get back. They are not searching for him, not even a little.

Haligtree soldiers are the only faction soldiers who are explicitly only found in the core of their structure- in Elphael. Godrick soldiers are found throughout Limgrave, Redmane soldiers are found throughout Caelid, Leyndell soldiers and knights are found in multiple places, etc. And Malenia remains at the foot of the tree, awaiting Miquella's return.

Likewise, they are guarding Elphael in such a strange way if they aren't guarding Miquella (and, again, they know he's gone). It's got some of the tightest security in the game in terms of how every possible path is a death trap that's absolute ass (that one stretch of Revenants at the bottom layer comes to mind) and/or a bunch of soldiers, along with them having multiple ballistae set up pointing at the paths someone would have to go down to get deeper into the Haligtree.

It seems that the Haligtree's guarding was intentional. For example, it's only after you defeat Malenia and the player tells Gideon that Miquella wasn't there that Gideon reveals that he heard the story that Miquella was cut out of the Haligtree. Gideon initially dismissed it and this is possibly why it's guarded like that- to hide that Miquella wasn't there.

My point is that the dog didn't bark. The Haligtree and Malenia did not react to Miquella being supposedly abducted, despite knowing he's gone, despite their continued loyalty to him. They instead expect him to return on his own.