FenixMarco has really good circumstantial evidence regarding Sabo's survival. Now, regarding Sabo not helping rescue Ace. There are many logical explanations for that. If you come to think about it, even Dragon didn't make any move to rescue his own son. Either that will compromise their operation or their location is just too far from Marine headquarters. Dragon even left his son for the sake of the revolution. I think Sabo was under the command not to make any moves in rescuing Ace. Imagine if he got caught while at marine headquarter, that world government would be able to extract valuable information from him about the revolutionary army. For the revolutionaries, their cause must come first above anything else. I think Dragon set an example by leaving his son. I can imagine Sabo's heart being crushed and weeping as he sees ace died on TV.