1) The game is finished by that point, there's nothing after that.
2) Let's be clear. The SGTs, as the MIDIs, don't contain any music. Only the data needed to play the music. The MIDIs have a simple set of instruments that any computer can decode and play. The SGTs are the same thing (with better instruments), but they need the DLS file to decode the music. So, no, you won't get to "extract" the MIDIs from it. MIDIs of FF8 DO exist, but they sounds crap... Square used original MIDIs for the music of FF7PC but they changed to DLS when they adapted FF8 for PC. With Samuel's soundfont (that sounds crap anyways), you can just replace the DLS file instead of all the SGTs and it will work.