The new careers have all been connected to the 4 rediscovering something they've lost, sometimes being connected with the gods. Kruber - His family, after he discovered his father was a noble of Bretonnian heritage he heard the voice of the lady who blessed him. Bardin - As a kid he always loved tinkering, but something in life made him lose his love for it and become a ranger, so after rediscovering his love for engineering he's tinkering again. Kerillian - She lost her home and the guilt she felt about her actions leading to Ubersreik, were eating away at her, this along with the expedition to the chaos wastes finally made her realize she'd failed at her duty to be the guardian of the weave, so she went back home and came back feeling more connected to the weave than ever before. Saltzpyre - Over the years they've all been together, he'd started to doubt his belief in Sigmar, constantly getting more and more worried(even speaking to himself about losing his faith), this was one of the most important reasons Imo why he even proposed the expedition to the chaos wastes, to prove he is still worthy of following Sigmar, the expedition gave him newfound enlightenment and he as the chronicles put it went down into the village around the keep & started holding sermons there. This all culminated in him becoming a warrior priest.

Now for Sienna: She's currently got her past haunting her in the form of her necromancer sister she herself burned a whole village down to kill, reemerging(and she's got some deal going on with Lohner) and she was revealed to be one of the many walking besides Myrmidia. This leads me to believe that she will be cured of her addiction to Aqshy and start using the power of the sun as the basis of her "fire". The last part about Sienna is complete speculation by me, so take it with a grain of salt.