The Kingmaker rule set is problematic, and we find that the best battles are not on the board but over the interpretation of the arcane rules. Here is the situation - Percy is in his castle and is besieged by a force large enough to match Percy plus the garrison. The event card is Bad Weather, so Percy is “under siege” in the castle. Then a force allied to Percy enters the square where Percy, his castle and the besieging force are. The allied force plus Percy, who will “sally forth” to join his faction in the battle, is larger than the besieging force - enough to get a 5:4 attack. There are three possible outcomes when the battle is joined and the event card is drawn, to wit 1) the event card says 5-4 and the besieging force is eliminated and some other nobles possibly die, 2) the event card says 3-2 or 2-1 or 3-1 or 4-1 and the battle is indecisive and possibly some nobles die, or 3) the card says Bad Weather again and no one dies. The question is, in situations 2 and 3 does Percy end the turn in the castle still under siege, or is he then outside the castle with his faction and allies? We are stuck on this one. Any wisdom from Kingmaker experts?
For non-VASSAL, game rules questions like this, I’d highly recommend posting your query in the forums for this game at Boardgamegeek.
Thanks. I’ll try that.
More rules questions - this time about executing royals.
Can a faction execute a royal before a battle that he is pretty sure he will lose to avoid ending the game?
Can he execute a King to avoid an Embassy on his turn?
Can he execute a King to avoid an Embassy on someone else’s turn?
Thanks. These are actual situations that arose in a game we just finished. I decided not to get into a rules fight and just let the very long game end (not in my favor.)
How did it go? I am just curious. 
I was a while ago, but as I recall we decided that Percy could not join the allied forces outside the castle unless they had been defeated in the counterattack. We’re moving on to another game now, as soon as we finish deciding about the rules we’ll be using. It’s always about arguing over rules it seems…
Great. It actually wasn’t just that I was curious. (The new website would not let me post such a short text and saying I was just curious was the best I could come up with.) Previously it was suggested that Boardgamegeek is a better website for rules questions that this one. I wholeheartedly endorse that. So I was wondering why you brought more rules questions here.
This website is more about the technical features of the VASSAL software and its modules. So for example if you said that the module was not implementing the rules correctly that would be a great question for this website - but we would have to trust you that your understanding of the rules is correct. (Although the first answer would be ask the module maintainers.) But if you ask a rules question about the game, someone may know the answer but I strongly get the impression they don’t. Which is why BGG is a more appropriate site. It has a lot more traffic and people go there to talk about games not game software.
Okay, so I know that I’m late to responding here, but I’m a Kingmaker fan, so I’ll toss my two pence into the discussion. 
Can a faction execute a royal before a battle that he is pretty sure he will lose to avoid ending the game?
Yes
Can he execute a King to avoid an Embassy on his turn?
No, once the card is drawn, the event happens. You could decide to do it right up until the card is drawn
Can he execute a King to avoid an Embassy on someone else’s turn?
No, see above
At least, this is how we have interpreted the rules. YMMV.