I think the death of Hoshi would be much too obvious, considering the preview. It looked as though they were either torturing her, extracting information from her, or both. But wouldn't it just add so much more depth to her character if this timid young woman actually survived through it? I think she's a great character, and she's totally useful too. She's already done so much more than Uhura ever did as Communications Officer.
So who's going to croak? If Enterprise does NOT get renewed, then they might just make him go out with a bang and a great impact, and die a heroic death.
I really hope Enterprise continues on, and if it does, I think it's going to be Mayweather and Reed to die. In my opinion, Travis is a talented pilot, but also...just bland and useless as a character. I liked the concept of his character at first--a space boomer that grew up on a cargo ship--but the novelty grew old quickly. He just hasn't contributed much to the series as a whole. If he has to die, I hope it's a noble death, complete with the cliche of "only the most skilled pilot ever could do this...but he won't make it out alive"...
I actually kind of like Reed too, but he's my second least favorite character. I can't put my finger on it, but I don't think he's that likable. Maybe it's the prissy British accent (which brings back nightmares of Bashir), or it's the fact that he got his ass whipped so many times (yet is still the Security Chief). Reed and Trip had some kind of good "buddy" chemistry going (and Shuttlepod One was great!), and it could have had some great development...if only the show survives.
So you never know, Reed and Mayweather might even die together in a blaze of glory. Imagine Travis piloting a shuttlepod through this huge firefight in order to accomplish this utterly important mission. Reed is along to make sure that weapon X will take out item X to disable the Xindi. Reed plants the device/blows stuff up/etc., and in an extremely dramatic getaway...they get shot down and blown into bits. The mission is a success, and Archer must reluctantly add more officers to his death count. Cue bagpipes and funeral.
Hoshi is the only other character I can imagine dying. Archer, Phlox, Trip, and T'Pol all rock pretty hard, IMO.