I actually love the idea of an alchemist character. It would kind of make sense to bring one, albeit not a horrific zombie-skeleton one, in order to actually locate and isolate a cure for the plague. I could totally see him as a money-grubbing friendless weasel that's totally vital to mission, knows it, and basically forces everyone to drag him around and protect him. Throw in a vague character weakness and a Scroogian "one thing I love more than money" mentality and you've got a fun little character to play.

Well, it's more of a whim than a suggestion, anyways.

Edit: Give him a thing for cute young girls like Pythia and you can even have him appear to be all creepy-stalkerish, then it turns out he lost his own daughter to the plague and is slightly more noble than he lets on. Probably the reason why he hasn't already turned tail and run.

Just spitballing of course.