So, Brubaker just let out that he'd planned to kill Bucky at the end of the Gulag arc anyway, and killing himself in Fear Itself just seemed a lot better as an idea. Given that Brubaker planned Bucky's death all along, I'm more certain Bucky's not permanently dead. Here's why
1) Brubaker's Cap run has been very well planned, with hints about Cap's death and rebirth coming from the very first storyline (Red Skull inhabiting someone else's mind to take over there body). So far bringing Bucky back has done nothing but given us cool stories. While that's great, and a good thing in and of itself, if he just came back for some years to die again he hasn't really accomplished anything with the character, nor really changed Steve with bringing Bucky back only to kill him off.
2) Brubaker's arc for Bucky since Cap came back has paralleled his first arc for Cap. An old villain coming up against him, trial and imprisonment by the US government, death, someone else taking up the shield. The next thing would be resurrection
3) Cap and Bucky. Seriously, to bring another Captain America book out with a mysterious narrator commentating on Bucky's life just as Bucky dies? The final reveal of the first arc is blatantly going to be Bucky still alive (even if he's not the narrator).
4) Nick Fury's being freed up just as Bucky dies. He needs a new secret black ops teams. He likes Bucky a lot.
5) Loose threads! To name just a few: Natasha and Bucky's relationship. That panel in Avengers #5 or #6 where future Stark (or maybe Maestro Hulk) congratulations the Avengers kids on not saying how evil Bucky is to his face or mentioning his future betrayal. Actually that's just two. I could probably think of more, but you can suggest your own.
6) Money! Killing off Bucky sells books. Making a new (ish) comic book character massively famous for the first time in a decade (seriously, think of another comic book character in the last ten years who could maybe hold their own series. The only ones who can currently are spin-offs of Wolverine and Hulk. Even Spidey's new spin-offs can't hold an ongoing. You think if Marvel managed to make an effectively non-existent character into this big intellectual property (and make one of their big three have a spin-off character who works) they're going to want him to stay dead? Marvel are a business, they're not going to bump him off for long if they think they're about to establish a working character. It's more likely they're trying to break him out of the shadow of Steve Rogers so he's even more a marketable character. A winter soldier ongoing? I think we can expect that.
So is he really dead? Maybe. Is that death permanent (or rather, is it only as permanent as every other comic book character's death)? Probably not.