First of all, 17 viewings down, and I'll hopefully be able to get at least 2 more in today to catch up to Nicole, though if she's still sick enough to miss going out tonight she'll get at least 1-2 in and pass me again. I'm starting 18 as I type, but I had an epiphany during viewing 17 about why the whole group dies at the end.
Near the beginning Block and Jons come across a corpse, and one that obviously had died from the plague. What if Jons at that point caught the plague from that corpse? Sure, Block had already been marked for Death in the opening beach scene, but Death at that point showed no interest in also collecting the squire's soul, only the knight's. So if Jons contracts the plague at minute 7 when he touches the corpse's face, he passes it along to Raval when he either a) roughs him up and prevents the rape of the mute girl or b) when he cuts him and prevents the torture of Joff. That would explain why Raval dies of the plague later (sure, he dies a bit before Jons but Raval isn't as healthy as evidenced by his obvious poor hygene, and he doesn't have the protection of Block's chess match), and also why Joff is not effected during that scene because Jons never touches Joff, only Raval. Jons could then pass along the plague to the mute girl when he shares the milk with her, Block, Joff and Mia at mark 56:00. Joff and Mia, if you watch the scene, only drink from the milk bowl before Jons does, so they wouldn't be able to get the plague from any backwash. The mute girl does drink after Jons, however, and she could have caught it then.
Jons could then pass the plague to Plogg when he gets hugged by him after their drunken heart-to-heart at mark 60:00. Plogg would then pass it to Lisa when Lisa kisses him during their reunion and the "death" of Jonas Skat. The only death that doesn't make sense in this line of thought is that of Skat himself, but if you remember that his intention is to climb up the tree to take a nap, it's easily possible that he falls out of the tree and breaks his neck, or that the tree falls over in the wind with his added weight in the upper limbs. Death's appearance in that case would be justifiable and wouldn't need a connection to the plague.
I'm not sure if this theory will hold up over more careful scrutiny, but it bothers me that Death takes all of the group at the end of the movie when at the start he was only looking to take Antonius Block.