First off, thank you Jen. There was absolutely no reason why this couldn't be talked out and the core of it seems to be perception and communication wires being crossed. I'm sorry I haven't weighed in on this earlier or posted over the weekend. I caught a cold, which bites.
I can't say for sure where the Underground will ultimately end up. Peoples' fates will depend on what they want to get out of the story. Given who Long Feng is, I would expect him to want to return to the kind of power he held before the takeover, at the very least. Whether that works or not, we'll have to see.
Something to remember, though, is that it took the Order of the White Lotus, bolstered by two comet-enhanced firebenders, to take back the city. They have powers beyond just being the League of Extraordinary Old Guys, they have what I like to call Plot Powers. The Underground's just got us, and none of us are master benders, so I would say it'd be pretty damn near difficult for the Underground to retake the city on our own.
Here's a little bit I found about the prison on the Avatar Wiki: "...The palace grounds contain the Ba Sing Se prison, a maximum-security jail made entirely of solid metal in order to prevent Earthbenders from escaping. Long Feng makes the claim that he built the prison as a solution to the growing crime epidemic within Ba Sing Se and believes that the criminals it holds are a direct threat to the Earth King, but in actuality, he uses the jail to imprison those who oppose him and the Dai Li and the criminals themselves are actually political prisoners punished for speaking the truth."
We had discussed that the place is heavily guarded, and pretty fortified. Toph, Sokka and the Earth King only managed to escape because Toph invented metalbending, and the city was in the middle of an internal coup at the time. Metalbending's the biggest boon they had and if Toph hadn't conveniently just figured out how to do it, the three of them would have had a MUCH harder time of it. Since the take over (which happened around three weeks ago RP time already), the Fire Nation has concentrated on quelling those that aren't taking kindly to the new management (and boy, that's a lot of people). As such, they would send a lot of soldiers to the prison to guard those unhappy citizens. Multiple break outs in this prison during the same day would also cause a heightened alert for the prison, and guards will be making more frequent patrols, and such.
Auka, ease up on the sarcasm, okay? In this case, I don't think it's helpful.
Joychi, I believe some of this confusion started from you perceiving the security in the prison as being a lot lighter than it actually is and that whole Jennomite mix-up. Please remember to keep balance given your earthbending training, and your environment in mind when you're fighting. The general rule of thumb is that we keep things as realistic as possible considering the kind of world we're writing in. We're not going to be able to pull off as flashy stuff as the canon characters, and we just have to go with good ol' fashion common sense.
Since the fight is over now, as far as I can tell (right?), I hope that these confusions have been cleared up. If anyone has any more questions about the prison or the general layout, please do bring them up.