(d32123 is a Marxist.)
Although the climax of the film reveals a much better side to Bane (he protected the young Talia al-Ghul from other inmates in the prison and as a result, was left disfigured and in constant pain), the film would be more interesting if it turns out Bane really did believe in his revolutionary rhetoric and was only using the threat of the fusion bomb to prevent the military from invading Gotham and crushing his little commune. Meanwhile, it's Talia al-Ghul who wants to destroy Gotham regardless, to finish the work her father Ras al-Ghul began in Batman Begins. Bane isn't interested in this, being both a sincere revolutionary and having been cast out of the League of Shadows by Ras as a constant reminder of his failure to protect his wife, Talia's mother.
To leave some grayness for Talia (rather than making her an ingrate willing to kill the man who protected her in prison), perhaps she plans to save Bane, the League of Shadows loyalists, and the genuinely-revolutionary Gotham residents (presumably as a favor to Bane) rather than simply killing everybody and herself. The only idea I've got to make this happen is perhaps letting it "slip" that the bomb no longer works, prompting the military forces outside Gotham to invade. She then persuades Bane and friends that all is lost and they need to get out of there. Then once they're a safe distance away, blow up Gotham, wiping out the soldiers and most of the city's residents.
At least that's the plan. I imagine Batman would have something to say about that. :D
Also, having the military invade Gotham would be better than having a bunch of police who've been trapped underground for five months Zerg-rushing Bane's goons without any tactical sense whatsoever. If Talia, Bane, and their loyalists are fleeing via some secret tunnel, that might also explain how Batman was able to sneak back into Gotham unnoticed.