If they were going to kill off any DISCO characters the ones that would have the biggest impact would be Burnham, Saru, and Tilly, and then Stamets and then on down the line. I'm leaving Culber out of it because I don't think they would kill him twice. That said, since so many of these characters have been underdeveloped and the series is now evolving into an ensemble show, I don't think it would be good to kill any of them off until we get to know them. That was one of the mistakes with killing off Airiam and having the crew grieve but we as viewers really couldn't because we didn't know the character, so it felt like a disconnect. There was a bit of that as well when Emperor Georgiou left. We hadn't really seen her bond with many of the crew so why were so many of them sad that she was gone?
If anything instead of killing any one off I think writing them off-like they did Nhan-with the potential to bring them back-is a better option. It could shake things up, while expanding on the new galaxy the series is creating (and also exploring). Instead of Saru returning to Discovery I wish he had taken command of another starship so we could see another starship/crew. (Though really I think it would've been better if Burnham decided not to be captain and instead lived with Book, with the destruction of their planet (note I said their because I would've had her living with him after Season 3), brings them back to working with the Federation. I don't think Burnham's first, best destiny was command. That's what Georgiou wanted for her, but Burnham's temperament and actions belie sitting in the captain's chair. I sort of wish they had had Burnham realize that she didn't really want to be captain after all and reject the offer. That she had found what she wanted/needed, with Book, and they could go out still saving endangered species while working freelance for the Federation and as unofficial ambassadors for them. The captaincy feels more like an end goal for Saru than Burnham IMO; I don't have a problem with Captain Burnham per se, but I don't know how organic it feels to the character we first met in the DISCO pilot).
If a character is going to be killed off, I see it being Book. I don't want that to happen, however, he's not a part of the DISCO crew, he's not even in Starfleet. He doesn't have a planet anymore, and no family-outside of Burnham now-so his loss could be played for a lot of drama and turmoil for Burnham this season or the rest of DISCO's run. He's been well established-more so than most of the DISCO regulars-so his loss would have an emotional effect on the crew but also the audience. I love Burnham and Book together-the best Trek relationship since Sisko and Kassidy, but I could see them sacrificing him-unfortunately-for dramatic effect. They can't allow Burnham to be happy for too long.
