So any allies of Turgall know to be looking for Kella and Arryn... what other facts about the pair are widely known? I can't imagine Blaithe's 'real' intentions are public (As far as anyone knows he's just freeing his magic absorbing sister from Mordecai?)
They could get wrapped up in the siege/betrayal somehow; creating a bit of conflict as to whether ro give them over for political power or not? (Assuming they don't escape!)