This has already been discussed a great deal, but here's the summary. McDonald, Walker, Jones and Hanrahan will almost certainly be tendered, although Hanrahan's closer status makes him a good bet to be traded sometime in the next eight months. Sanchez is very likely to be tendered as well, since he's a good platoon partner for Jones and since there isn't much reason for the Pirates to have changed their assessment of him since they traded a compensation pick for him in July. Resop will probably also be tendered since the bullpen is a bit thin, although I think non-tendering him and looking for something better on the free agent market would also be a defensible decision.
Morton will likely be non-tendered. After having Tommy John surgery last season, he likely won't return early enough and hit the ground running hard enough to be worth $2.6 million. It would not surprise me, however, if he remained with the organization.
That leaves Karstens. As I've said before, I don't think non-tendering Karstens makes a lot of sense, given the amount of uncertainty in the rotation. If the Pirates do non-tender Karstens, I'll be uneasy, but we would have to reserve judgment until the offseason is over. It's possible the Bucs have more tricks up their sleeves. Even if they feel they might be able to get someone through free agency, though, there's space for Karstens. A.J. Burnett, Wandy Rodriguez and James McDonald are the only names written into the starting rotation in ink. Burnett and Rodriguez are old, and McDonald is inconsistent. As I think someone pointed out in the comments a while ago, if the Pirates were to add Karstens and someone else to that mix, there would likely still be starts available for Kyle McPherson and Jeff Locke, and it wouldn't be hard to find a spot for Gerrit Cole at midseason. Also, for the Pirates, having to depend on the free agent market isn't usually a good idea at all. So unless there's something in Karstens' medical record I don't know about, tendering him looks like an easy call to me.