You mean, other than the fact they have already introduced the seme's killer . . . . .
Well, yes as I said, that one sentence is why this is tagged as tragedy. But it's possible that this sentence doesn't mean what we think it means since we don't know anything else about it.
There's also the fact that modern medicine can do wonders. A person might technically be dead for a short time but then the doctors get the heart beating again. Yes, I'm an optimist >_>
That's also an option ;) and considering how much this author likes to play with our expectations it's very much possible that this is what will happen.
Don't freak out because of the tragedy tag. Of course it's possible that half of the cast will be dead by the end of the story but nobody knows for sure. The reason why this tag is there is because of that one sentence. Whoever added it doesn't know anything for sure either.
This story isn't finished and there are only a few more chapters in Korean than there are in English.