Apologies for slow reply.
Is Redcloak evil just because of the impacts of going through with the plan, or is it just a smaller part in his overall evilness? I think the latter. Trying to kill Durkon is justgoodpractical (evil) business, weighing various risks against each other just like killing Tusikko.
There’d have been tangible benefits to him (successfully) killing Durkon. He wasn’t just any random diplomat, he was a previous enemy directly trying to stop him. Waiting or reconvening if Durkon is the distraction to a trap is also a risk to the Goblins.
If he thinks that the old gods might be genuine about the offer, it’s reasonable for Redcloak to think they’ll send another messenger, as it’s too important to them to rescind the deal over one shot messenger. He probably doesn’t know that the old gods are restrained from discussing the Snarl with their followers, given that the Dark One doesn’t seem to be bound by that with him.
I think the quote below puts it more eloquently than I can, that Redcloak is a not one-dimensional character solely based on “the sunk cost fallacy”, and I think it’s a bit sad that he keeps getting reduced to that? IIRC Miko got a lot of hate, but similarly it’s the characters flaws that make it an interesting story. Sure if it was a game where players had to negotiate with Redcloak the NPC to get a victory, it’d be frustrating because it’s not in the player’s hands. Maybe that’s why I have’t not tried to pay too much attention to learning the D&D details, so apologies for not responding on appropriate spells he could have cast because I have no clue there, I’m just here for the story (probably a very small minority, I’m aware)