I always got the impression that Dart really liked being a dad. That being with his new family took away some of the pain from what had happened, just... not enough. I don't think he was really obliged to stick around for as long as he did. Serrin and Talmah could probably have raised Bowki on their own just fine. Dart didn't want Bowki to know about what had happened in the past, I think that if Dart had stayed out of wrapstuff he wouldn't have been able to keep the truth from his son for much longer. Sure, Bowki might've learned the truth later on, but when he was an adult, not while he was still a cub.