Nana doesn't have any idea that Ren's on drugs right? I think when Nana finds out from everybody else she'll realize that she really didn't know much about Ren.
Dont think she even know that he used to take drugs and got clean. Dont think they will tell here for while though, she will probly crash hard enough when she finds out about the car crash.
About the "Ren is alive" thing, i have done some backtracking in the manga to look for clues. So far the only thing i have found is when Shin and Yasu are talking in the car (dont remember what chapter it is) and Shin says "Hachi think that Ren was the one who droped of the photos". Now, Yasu seems pretty chocked by that, Hachi probly meent that Ren drop it of as a "guardian angel" or something, but there is a tiny, tiny, tiny hope that Ren is alive... Guess we will find out in the next one.
EDIT:
Takumi: Oh, hi, Nana, guess you heard that Ren smashed right in to a wall in 150 km/h?
Nana: *hysterical crying noises*
Takumi: Yeah, eh, one more thing: Ren was pretty much snorting anything he could get his hands on, tripping balls so to say.
Nana: *hysterical screeming crying noises*
Takumi: And we are pretty sure he had a thing for Reira to...
Yeah... it would kind of suck to tell her that
