I can find a few reasons why the guard would choose to not execute Lance, even if no one mentions any of this in the game (totally possible). I think one of the most important reasons could be Lance’s allies and the past. Lance wasn’t alone in this war, he had enough people agreeing with him to be able to form an army and almost win a war, that’s A LOT of people who think like him. It’s not like he bought some mercenaries or owned an army from the start, everyone there had something against Eldarya. During chapter 26, Erika notices that most of the people with Lance are faeries who suffered from crimes of the guard or other faeries. If we look back, all these crimes started with the Blue Sacrifice, with faeries hunting daemons and aengels for not sacrificing as well as faelines with dragon blood in a failed attempt to bring balance to their new world.
If you think about it, what happened with Leiftan, Lance and all the faeries who sided with them, was a consequence of centuries of crimes against specific races going unpunished or the guard punishing those who opposed their ideas or refused to obey.
Now, they could kill Lance, but they would be left to deal with a whole army of faeries who lost their leader and not only that, but he’d become an example of how the guard deals with his problems by killing everyone who causes them. That was their modus operandi before Erika arrived.
They would also have to persecute and kill every faerie that sided with Lance and still shared his ideas. In the end, they wrote that war as if it was a war of good vs evil, when in reality, for many chapters, they’ve been mentioning the guard committing terrible crimes and in the beginning of the game we saw first hand how much they screwed up things, but all of this was forgotten to paint the guard as “the good guys who want to save the world and never did anything wrong”.
Now they had another sacrifice, the White Sacrifice. Three people sacrificed this time (Valky, Erika and Leiftan) and now food is nutritious. If they killed Lance and started persecuting all his allies, they’d basically be starting this new era, this second chance, with another genocide. In a real world scenario, this would be impossible, but the best solution is to simply forgive everyone. Lance’s side has to forget everything the guard and faeries did to them and the guard must move on from everything that happened. Maybe this is why Chrome called it an “era of forgiveness”. Everyone should make amends and work to atone their sins, but I think killing as punishment or “justice” would be a very bad idea long term looking at the history of Eldarya. Actually, maybe some of the new characters we are meeting could be Lance’s former allies who fought in the war.
In the end, we’ll have to wait to see the explanations of what happened after the war, but I think this could be one way to explain it. Of course it shouldn’t be as easy as simply forgiving everyone, this process should take years and tons of conversations.
Thank you for coming to my TED talk.