I chose to SPARE Modron – and I believe that is the best choice – although the consequences for either choice are not dramatically game altering. So if you really want to kill Modron – I would say you can safely do so without serious repercussions. With either choice you get the alliance- and get a Raven on your alliance map and the main story moves forward. With either choice Twydyr thanks you and calls you a friend. With either choice the same man dies in the wicker man sacrifice. The downside to killing Modron really seems to be orphaning a child and weaving violence and revenge deeper into your DNA.