He knew he needed to get Gabriel. Even though the old man claimed that they weren't going back, that didn't mean they were going to go back to the world.
It was also quite possible that by the time they returned to this place, the Crews would already be waiting to take them home. It was possible that they weren't going to be allowed back here.
If he still tried to come back after everything was over, the scrutiny on him was going to be over the top. Especially since this is the time when he killed Mander.
"Get inside the ship!" The old man commanded. All the participants started entering the ship… All except one.
Instead of flying inside the ship, Lucifer started flying back to the world.
"I forgot my lucky charm in my room. I'll be right back! Hold the ship for me!" He informed the old man, not even waiting to hear his response.