If.

Being that I'm not part of the Titans, nor would I be a good one, I can't say I know how they will end up. This is mostly speculation, made by my own options and obsrevations, which are subjugated to change as new evidence provides itself.

My current impression on the Titans is not good, and by that I mean I don't think they're very good heroes. As I've mentioned, their attitudes makes them very bad candidates to serve justice. Their actions, and the reasons for it, likely won't be for the best. Right now I have the impression that they don't have a "Don't kill" rule; I'm pretty sure the only reason they haven't killed anyone was because their first opponent was a giant robot, and they couldn't land a clean blow onto you. Killing Serenity will either make them go into a rage, giving them very little inclination to hold back, or possibly make everyone get very serious and think of how to not get revenge, but to bring both Jack and the Shadow Complex to justice. The latter is what I would consider the "Best" option, as it bring a sense of maturity to the team while still being "Good". 

Because while I am no master of the law, if you do kill Serenity, you murder a teenager. For money, at that. I'm pretty sure being an bounty hunter is an illegal occupation, even if killing Serenity was not your original intention. Additionally, Serenity could also fall under the category of 'Endangered Species" as well as "Government Associate" due to her membership with the Teen Titans. This may brand Jack as a terrorist, which will flag his entire family if his identity gets discovered some how. Postmortem possibly. Even if they're completely normal people, they're still his family and thus associated with him.