First I need a clarification on the triggered ability of Bronn: it is an ANY PHASE, so I think I can't use it as a "save effect" if I haven't payed the gold cost in an "appropriate window".
And then the question: I attacked in a claim 2 military challenge and my Lanni opponent has 3 characters (including Bronn) and 2 gold in his pool. My opponent decided not to pay the golds to activate Bronn ability. Then I used stealth on Bronn and the challenge was unopposed, he chose 2 targets for the claim effects, then he knelt Bronn to play "A Lannister Pays His Debts" on one of my character. At this point he declared to pay 2 gold to save one of his characters chosen for the claim effect and stand Bronn...
Can he really do that?
And if the answer is "No", could he do this (play the event and THEN save one of his characters) if he decided to pay the 2 gold before the victim for the claim are chosen?