If the Thaum changes to Lancer, then someone else in the party can switch to their Thaum. The point of this job system is that everyone can change class on a whim to fulfill a need. So, just hope that maybe your Conj. or Maur. or someone can change to Thaum. And with this exp system, I think a lot of people will be leveling many jobs. Well, we did anyway in FFXI.