Story is definitely interesting. I want to know more about their past, the new girl's past, why're still alive, what happens if the girl goes home to her abusive father's place, how they can interact with objects etc. Art is pretty nice too
I'm not sure they are dead at all. I think it might just be that they are treated as such because they don't interact with people and most people don't know they are there. That said, Tsukuma clearly said he killed himself, but he also told Sakura to go back home. Sakura doesn't seem to regard herself as dead.
Either way, so far we have only directly seen them interact with other "leeches".
The fact that they have to avoid being in someone's house when they are there seems important, as does what Sakura says when she walks past people in the street. It also seems like they bought fast food, and that Sakura is able to sell things, as she mentions with her ring.