[A tragic moment Lucifer won't get to witness initially, not when he's got his own business to attend to. But eventually he does remember this... situation at hand, and does start to grow worried. He can't exactly trust Sebastian to do the right thing, not when he appears incapable of even knowing what that thing would be.
So he'll set out to find him, hoping his first attempt to search by the forest would be right. Otherwise he's left to do Dad-knows-what and that'd be a lot more difficult for everyone involved.]