When you return to the SMC in the second Act of the game, you'll find yourself in the Spetzes Sector. If you ask around, you'll learn Celina is also around. After locating her, you find her ship is damaged, undergoing repairs. Nikitas has been captured, at this point. You can choose to help Celina save him, or move on. Don't be selfish, regardless of what Celina says. Her ships in poor repair because of the pirate that managed to capture Nikitas. Save the fellow, and you'll be sure to see him and Celina later in the game. Additionally, you learn later that Celina played no small part in keeping the crew that got left in the SMC safe and sound... so you pretty much owe her. Something tells me that if you don't help you don't see either of them later on... but I'm not really willing to play through the entire game to test that tiny therory out. To each, thier own.