I wouldn't say it's "open ended" honestly. Sangwoo definitely dies according to what the author shows us. He was smothered to death with a pillow when he was helpless to stop it.
As for Bum...that one IS a bit more "open" but the conclusion is he commits suicide by stepping in front of a oncoming bus.
So unless they get isekai'd to another world, I don't see this continuing. Sorry if this doesn't feel right to some of you but I'm basing this off what we're shown. ya know?
* I am so sorry but I was mistaken about Bum's ending. Idk why I thought I remembered him being struck by a bus but that must've been my own head cannon since it ACTUALLY ends completely open with only the green "walk" sign switching to a red "Don't Walk" sign. (basically implying something like he gets hit but never showing it outright) so Bum's ending IS open and could be made more of if Sangwoo wasn't cremated like the man said~
Did they actually both die? I’ve re-read this about 5x and I still can’t tell