As the topic says: how would you handle it, especially cohesion-wise?
The given situation is that I got the KT into a longer mission (which might evolve into a mini campaign). One player, who plays an ultramarine and usually is the leader (given his high fellowship bonus) could attend the first game session, but will be joining us tomorrow. It might happen that the current leader will want to give the leadership into much more capable power gloves. The team's cohesion is now at 0 (down from 3 due to some blast-damage). if the mission had started with the ultramarine leader it would have been 7, so now they'd have 4.
Or perhaps changing leaders mid-mission is a bad idea, for fluff reasons etc? What about changing oaths? When the mission started it seemed like an escort but due to unexpected (by the KT )events it is now a lot more complicated matter.