I respect Gotti for standing up for what he believed in. No way his ego lets him flip. Lets not forget he still had family involved with LCN who could have been hurt if he flipped.
In the governments eyes yes he was the biggest fish, but IF he flipped, he could have brought down the WHOLE Gambino family which if I'm a prosecutor I would want more. Taking Gotti down didn't really kill them at all, it was testimony that hurt them most not losing the boss. But in those days I just don't see the feds even trying to get him to flip as he flat out made himself "the target".