Yeah if we go they were losing about as much as germny lost in actual ww1 which was 4% and 2.5 since ww1 lasted 4 years and this one is 10 its a loss of probably at least 12% percent of the population, how nice.
Yeah, how i understood it is that if the mc choose the kang sieun route she won't disappear but in my opinion the best option is letting her, its sad but the dead will stay dead.
Nah he did slice his arm, its just he thought of the hypothesis his body isnt his original one so it wouldnt get injured as he says its a specially made body as he thought.
Since she is mammal i will have to guess the tail is just a normal mammal tail with bone,nerves and muscles with a keratin armor that makes it look like a scorpion tail with may be even poison as platypuses have poison and are mammals.