Didn't you know? Only old people die in shounen anime.
I kinda imagine as far as Mr. 3's situation goes... he wanted to get himself to the scaffold, but he didn't really have a plan of what to do once he got up there, so he was kinda forced into just playing it by ear. Obviously Mr. 3 wouldn't have been capable of freeing Ace right there in front of Sengoku, and any deviation from instructions would've revealed him, too.