An online friend expressed disquiet at how Laios seemed to be way too happy-go-lucky on the way to the dragon encounter (basically, the entire anime before this episode), and seemingly not as devastated at the revelation at the end of this one.
I countered as follows:
I think Laios really wants to save his sister: that's the main reason behind this dungeon crawl to begin with. however, not only is he saving effort (doing on-site procurement) instead of lugging along enough food for the trip to and back, but also he's enjoying the trip in whatever way he can. I think it's because he's of the opinion that there's really no use in worrying as there's nothing much they can do other than to "try to defeat the dragon and deal with the situation afterwards."
I think the latter half of this series would revolve around this "dealing with the situation" as their optimistic plans at the start (revive his sister once the remains have been found) have proved to be somewhat lacking.
They might need to find someone who can revive his sister given what's left, or failing that, summon her spirit and have her inhabit a replacement body (so, necromancy, I guess).
As for the lack of a reaction (given how it came at the very end of the episode, I doubt it's even shown), I think he's just in shock. It's pretty natural, I suppose that one's reactions might seem muted on the outside even though you're distraught on the inside. I'm looking forward to how Laios deals with this situation, and what he might come up with next.
Edit: I pressed enter too early, sorry about that.