Finch blinks, looking to the gnome and then to the elf. "The undead are real enough. First time I saw'un, I prayed to Apellius. Still hasn't answered..." he pauses, for a moment, and then continues on. "I don't know much 'bout this masked fellow, but the stories yeh've heard are true. Magic an' metal, how they do it I'd rather not find out...As fer how they make more, well..."
He trails off a second time, scratching his neck. "Lots of'r men, if they don't die in battle, they sicken. Sometimes they rise, if y'don't burn 'em after. Sometimes they don't."
It's fine, I'll just have to ask that you don't ham it up too much.
I do, occasionally, have a tendency for my games to get too dark, so a little comic relief couldn't hurt.
Now is a good time, I think, to discuss two things. First, is the disease mechanics! (and as an extension, maybe I'll talk about undeadifying a bit!)
Disease and poison both function on the same rules. You get a "health" check which, true to its name, takes its modifier from your current health score (treating the health as an ability score, for purposes of determining the modifier). So Fibleck, who's current (and max, since he has no injuries) health is 14. If he were to decide to pet a disease-carrying rat at this moment, he'd get a +2 to the roll to resist catching it. If he were injured, let's say by 4 points, he wouldn't get a bonus at all.
Now, since healing is rather difficult (it takes time, and first aid/regular medicine only aids in this recovery), soldiers grow more susceptible to disease as the war rages on. After a few battles, Fibleck might find himself with a few cuts: His health is now at 9. If he tries to pet the same rat, he'll take a -1 to the roll.
Recovery from a disease is checked on a daily basis. Since many of the more deadly diseases cause health damage, they become progressively more difficult to recover from as time goes on. With the right medical care, however, a bonus can be applied to the check to fight the disease- and this damage circumvented. A ghoul, which is a specific type of undead, might inflict its victim with a disease that, upon killing said victim, causes the person to rise again as another ghoul. Fun stuff.
Of course, without the relevant knowledge, no character will be able to tell the difference between a ghoul and a zombie, or the various diseases and effects of those diseases that they might carry. If you come across a soldier who's hacking up blood on a scouting mission, for example, you will have no way of knowing if its safe to let him take the night shift, or even take him along, during your three day-and-night journey to report back to command.
The second thing I figure I'll ramble about, is the tone of the game and my DMing style.
As I've said, the game is rather serious. But as I've also just said in this same post, comic relief is A-Ok. Despite the fact that you're basically up against unfeeling robot zombies right now, I can and will be throwing ethical problems at you at various points. I'm a huge fan of the trolley problem. Similarly, I normally won't hesitate to venture into some more mature subjects- genocide, racism, and I guess if you wanted too you could technically visit a brothel or something but I sure as hell won't roleplay that with you.
The plot has rails, but there are multiple rails and you may choose to follow any set of them or none at all. I will adapt. In fact, you could decide to desert the army during this prologue, if you so choose, but I'd much prefer it if you you found a reason to not do that.
You're also free to split the party at any time, though I also must ask that you at least try to avoid doing so for at least a chapter or two.
Going back to the rails rambling: I have basic plot outlines for the prologue, and first two or three chapters. The world is a living thing, so even if you choose not to fight the undead or whatever, they'll still keep doing their thing. Maybe by choosing to fight you'll make a difference, maybe you won't. Maybe by choosing to flee the front lines and take refuge in the Freewater holds, you'll end up doing more to save lives than you ever could have done fighting in the Triumvirates army. I don't know, this sort of thing is up to you.