The articles from White Dwarf are a good example of solid campaign progression, if you have the will to make it so. All the progression is quite explicitly steered by the happenings on the table.
Injuries and daemonic possessions and kit acquisitions get represented on the model, new skills and abilities get added, and the odd number gets changed to better represent.
Mostly though, given not everyone wants to rebuild the models for every game, it's a roleplay thing.
If the antagonists clash over an artifact, the one that escapes with it in their posession maybe gets ambushed while rendezvousing with their antiquarian as the next scenario.
The bodyguard, with his reputation tarnished, is perhaps a little more die-hard (that can be a new mechanical Ability, or just a tendency to go hard in the paint), or the attache has decided that maybe this isn't really worth getting killed for (losing a few points of Willpower, or just developing a strong tendency to tactically utilise solid cover).
Obviously, the seneschal who lost both legs to a force-sword swing, he's walking fine on his remarkably-similar-looking bionic legs - but he's no sprinter since The Incident.
