Bruce flies the ship out, most likely ejects and puts on autopilot, goes to Spain, sees Alfred, nod and wave, no words said, Robin is introduced.robin is the detective, the lady at the place says,"You should use your real name. Robin. I like it"
Joker is caught, Two-Face is killed, Batman and Gordon decide it is better to leave the city in the dark about what really happened to Harvey Dent (Two-Face) as so the new Dent Act would not be retracted. The Dent Act took out almost all organised crime in Gotham, which is why Gordon and Batman wanted to preserve it.
I like that the Joker wins in the end. It doesn't matter that the passengers on the boats chose not to blow up the other boat. The only reason they did that was because they still had hope in Dent. So, the Joker shows that he can bring anyone down to his level, thus leaving Batman is a lose-lose situation. Either he tells the truth about Harvey Dent and causes the people to lose all hope, or he takes the blame and leaves Gotham some hope but rids it of its only protector. Also, the Joker is a bit of a liar; he claims to have no plan, yet he obviously has a very well thought out plan.