I looked at all the chapters again and yes, everything points out Ren's death, but there is just one suspicion (I found just one).
Chapter 66; "Hachi said she thought maybe Ren had snuck it into the mailbox." So, little Ren can't do it, 'cause a few pages earlier Hachi clearly said that little Ren is in London with Takumi. So, maybe, like Nana's situation, Ren's state is not uncertain either? I hope it is. -_-" But I feel like it isn't like that, maybe they were just trying to say "A miracle happened." or something like that.
And little Ren looks exactly like Shin. I still can't believe he's Hachi's and Takumi's son. -_-" Whatever, I should just read next chapters. -_-"