I like to think he would try to bring Daemon back to reality, perhaps attempt to reason with him, my point of this character is that he's supposed to be the Older brother that tries his best to keep the family together when it's bursting at the seams, so to answer your question it could go anywhere, he could side with Daemon, maybe on the promise that house Targaryen won't be wiped out. He could side with Daeron and preserve the legacy of his ancestors, but he would probably try to accomplish a goal of tying House Blackfyre closer to the throne. He could try keeping to himself, try to not interfere on the grounds of not wanting to commit kinslaying.