The original ending was that Keating was dying of leukemia, hence his 'carpe diem' philosophy. Mr. Perry sues both Keating for corrupting Neil, and the school for compensation and emotional suffering. Todd and the other 'Dead Poets' are told by Mr. Nolan to testify against Keating, in exchange for a clean record of any wrongdoing. Cameron is the only one who testifies against his former teacher, feeling that the school needs a scapegoat. Instead, the rest of the boys defend him and explain that Neil chose to act on his own beliefs rather than be influenced. Keating is acquitted of all charges, much to the fury of Mr. Perry, who spends his last years in depression and sorrow over the loss of his hopes for Neil and his "legacy." The boys are put on disciplinary probation, while Keating goes into hospital as his condition worsens. At the end of the film, Keating dies feeling that he has made a difference in the boys lives. The director changed the script to emphasize more the boys' personal journey, but he has stated that he wished he had gone with the original ending.
I don't know how accurate that is, but I certainly would have found that preferable to the real ending. It probably would have made for a pretty long movie, and it might well have bogged down in the end. And anyway, here's how I would have ended the movie:
MR. NOLAN: I said leave, Mr. Keating.
Keating slowly turns and heads to the door. As he opens it, Todd, stands upon his desk and turns to Keating.
TODD: O Captain! My Captain!
MR. NOLAN: Sit down, Mr. Anderson!
Keating pauses at the door and looks back at Todd on his desk.
MR. NOLAN: Do you hear me? Sit down! Sit down! This is your final warning, Anderson. How dare you? Do you hear me?
After a moment of indecision, Knox climbs up onto his desk.
KNOX: O Captain! My Captain!
MR. NOLAN: Mr. Overstreet, I warn you! Sit down!
Pitts climbs up onto his desk, followed by several others, including Meeks.
MR. NOLAN: Sit down! Sit down. All of you. I want you seated. Sit down. Leave, Mr. Keating.
More students stand on their desks until half the class is standing.
MR. NOLAN: All of you, down. I want you seated. Do you hear me?
MR. NOLAN: Sit down!
Keating stands in the doorway, staring up at the boys in wonder. A
smile comes to his face.
KEATING: Thank you, boys.
KEATING: But really, you've all thrown me under the bus already to save your asses, I've already been fired and now that emotionally stunted turd Mr. Perry is gonna sue the living shit out of me as though it's my fault his gutless kid killed himself rather than stand up for himself, and I'm supposed to be happy because you stood on your f***ing desks? Here's a life lesson for you, boys: Suck it.
Keating exits, slamming the door behind him. The boys just stand there on their desks, looking at one another. Finally the one named Knox (whichever one he was) turns to Todd and mouths the words, "What the f*** do we do now, genius?"
Fade out. End credits over some Grateful Dead song.
Yeah, that woulda been an ending for what has become one of the most overpraised movies ever made.