Alas the chances are quite good then, I fear. Though to be fair: in Fiat Justitia, I achieve it by letting one general move somewhat slower in a spontanous situation. Executing Fritz, by contrast, would have given FW ample opportunity to think, and consider the consequences. Renember, in rl, Frau von Kameke saying "don't be like Peter the Great of Philip of Spain" had a sobering effect, and both these precedents were also impressive because the monarchs in question ended up having no son at all to pass their Empire on to. (Peter had two more other than Alexeij when killing him, but they both died. Hello, century of Czarinas.) FW was just the type to believe God would punish him for a son killing by taking his other sons if he has time to think it through. If he's in the same room with Fritz after having learned both Katte and Peter have made successful escapes, and Fritz, full of relief about that, can't resist taunting him, all bets are off.