I do agree that Emil is behaving very oddly since the start of the chapter. And I do agree that he appears cold and detached but I want to point out emphatically that the list of behaviours (listed by Lazy8 for example) highlighting his empathy are his normal response to minor-to-middle-sad situations that do not involve him personally.
This is not a minor-to-middle-sad situation. This is not a normal situation. This is a situation that pushed Emil's world off-kilter, and that lines itself up with other horrifying experiences during the course of the comic – and Emil's response to those is different. Take the first raid for example: He panics, he acts unrationally, he vomits, he sleeps. These are all reactions to shock. Please note, how noone finds it odd at this moment that Emil sleeps. It is assumed that he is mentally fatigued because he just experienced shock and genuine mortal fear.
Then he bounces back to his seemingly usual self but note that his swagger about going into troll-infested areas is gone. It was gone already after the Dalahästen-incident, but now he is cautious and inclined to shirk possible nests altogether (see: Sigrun's crap-building talk and Emil's reaction to the deer and the cat-noises).
I am glad that some other people already pointed out the possibility of a severe shock because I genuinely believe that Emil is experiencing a version of shell-shock. He is dull to the point of stating the obvious (compare this to page 616), he is exhausted to the point of sleeping in a potentially dangerous situation, he is unresponsive to negative experiences like being kicked awake (highly embarrassing situation, but apart from a hand in his hair no reaction) and being rebuffed once again by Lalli.
It is not „only“ the things that happened in chapter 15, that have lead up to Emil's unresponsiveness, tiredness and dullness.
The situation in the comic now comes after months of exposure to a row of jarring experiences which touch on everything in Emil's world. Piece by piece Minna has taken things that Emil takes for granted and has destroyed them. She even started before the Comic started in taking financial security away and in the wake of it Emil's view of himself as being clever and likeable. (The fact that he came up with an explanation that shifts the blame unto others still highlights that he knows that something is wrong and tries to find an explanation.)
Step after step Minna challenges Emil's beliefs on: Safety and Security (Troll and Giant encounters), Physical Integrity and Duration of Life (Sigrun's wound, Tuuri's wound, kittens, Momma-cat, Cuthulhund), Magic and now Friendship and Truthfulness.
Take a look at the interaction between Sigrun and Emil on pages 669/670. It is the first time we see them interact again after Sigrun vented her anger on Emil. Even though he responded on that occasion instinctively right (pointing out that he was doing his job) the relative coldness on pages 669/70 shows that he is not sure where he stands with Sigrun anymore. In the following weeks we see him less and less next to Sigrun (f.ex. standing quite a bit away when Sigrun and he watched while Tuuri repaired the tank) and more often in company with Reynir and Lalli or only Lalli.
Please note also that Emil is not great on social interaction: we rarely see him interact with Tuuri or Mikkel and really badly with Reynir. So, after being chewed out by Sigrun he is down to one person he considers a friend. Then he tries to reassure his feelings of friendship with Lalli at the worst possible moment in the worst possible manner (Aliax has written a very good short essay why Emil really had no idea about Tuuri's dire situation) and consequently gets rebuffed by Lalli.
Emil does here what he did after the soup-incident: He gives Lalli space and probably plans to engage in careful peace negotiations later on. Only that later on Tuuri kills herself and Emil is confronted with the knowledge that the whole squad lied to him about Tuuri's condition and that he cannot trust anyone's (but Lalli's) behaviour to be truthful. From his point of view, someone who broadcasted a solid signal of positiveness and acceptance of life suddenly killed herself, while others also broadcasted that nothing was wrong, knew all along that everything was wrong. This is a breach of trust of epic dimensions and I can easily imagine that Emil is now so deep in shock and disbelief and hurt that he has not even registered what he has done when he made his little pep-talk in the store. And even if he does, it is possible that he thinks that Lalli doesn't want to have anything to do with him anymore (let alone a lame and totally insufficient apology).
I am convinced that Emil's behaviour now is a way to show that he is not ok at all and should not interpreted as a sign of fudged storytelling by Minna. Remember how she explained that Tuuri's death was necessary for the things that were going to happen later in the comic. Just killing off the Tank would have been enough if Minna wanted to write the rest of the story about the crew finding their way to the coast – neither Tuuri's injury, nor her death are necessary for that. So what changes with Tuuri's death? All relationships within the crew. And in doing this and letting the persons in the crew experience and act like they do Minna hurls them all into emotional trauma one way or another and Emil being bland and uncaring here is one sign of that.