Long distance and quick draw Fern to one shot is really a force to reckon with.
It is possible that she deliberately not try kill, but it is possible that she also simply failed. I think it would be out of character for her to really go for the kill. We already saw this kind of magic not dealing a lot of damage against human clothes with magic resistance, so it makes sense.
In the last chapter, we saw that Sein relative power level with the Goddess magic is probably higher than the shadow warriors priests. So the group is quite strong and more balanced in its own right.
I do not think Serie would die here. Her intuition never fails and that is her main perk, but we don't know how far that would extend to. She knows almost all human magic and she said demons feared her power in the mythical era.
As far as we know, only Fern (and probably Frieren too) knows that Serie restrains her mana and do it better than Frieren. So for her to hide part of it, but still display a large output anyway could be a 4d chess move.
But we know that pure strength could easily overpower a mage, so there is still a way.
My though on Sense statement that elves are arrogant towards death is that she is wrong. Serie and Frieren witness the end of the elves civilization and saw a lot of human death, so they know they could die. Both lives in seclusion and not really showing off for centuries, so to not attract too much attention.
We don't know exactly how Minus died nor why. So it is hard to tell. Kraft is also roaming around. But as a monk, he may never be targetedline Serie and Frieren.