"Imagine that the Sonic game franchise is ending forever.  If you were somehow put in charge of directing the Last Sonic Game, what would you do?"

I froze, stunned.  How had I not ever thought about this?

What has followed is a waterfall of ideas, some from my own head, some from friends.  It ended up being pretty dark, probably rated T.  Now I want to gather everything up and write a fanfic.  Here's the jist of the story so far:

The game opens with Robotnik having just won the long battle against Sonic and his friends.  Sonic is badly injured from the fight.  Despite his upper hand, Robotnik hesitates at finishing off the hedgehog, and Tails takes the chance to airlift Sonic out of the metropolis and into hiding in the wilderness.  Robotnik does his best to keep a straight face as Tails disappears, and chooses not to send flying robots after them, instead shouting through a megaphone "Never come back!"  Here we see a bit of character development -- Robotnik may actually be a nice guy on the inside.  (My goal is to make the player connect emotionally with him.)

Two years or more go by, with Sonic needing to undergo rehabilitation to reach his original blinding speed.  The first level would be a lovely 2D Green Hills-type zone, consisting of obstacles set up for Sonic's exercise.  After the player completes the level, Sonic concludes that he's ready to get back in action.  Tails agrees to follow Sonic to the end, and Amy swoons.

That night, we see Robotnik in his mechanical castle, more depressed than ever.  Over the past couple of years, even though he has conquered most of the planet with his robots spreading like wildfire, he has become increasingly lonely and miserable, missing the old life.  Being at the top is apparently not all it's cracked up to be.  Robotnik accepts dinner from a butlerbot and watches the television.  The broadcasting is nothing but happy material meant to brainwash citizens into loving their dictator.  He turns it off and sits in silence before putting his head in his hands.  He appears to be feeling incredible guilt.

The game progresses.  Amy and Sonic actually have a sit-down talk, and Sonic manages to tell Amy that they have no future together.  Amy gets up and goes into her hut.  More of the game passes, with plot I'm unsure about.

When the story is spiraling upwards, the player reaches a boss fight with the same giant machine that defeated Sonic at the beginning.  Sonic reaches a breaking point, and at this critical moment Tails jumps into action.  The player controls Tails and defeats the boss.  But in the following FMV, after meaningful and distressing dialogue of how Tails always wanted to prove himself and this is his chance, Tails is killed.  Robotnik is shown in his machine's cockpit, horrified.  He detaches from the machine and flies away in his eggmobile, leaving a stunned Sonic lying on the ground.  Knuckles appears and helps Sonic leave the city.

Amy is waiting when they arrive, and quietly informs Sonic that she needs to leave if she has no hope of having a future with him.  She turns around and starts walking away, but Sonic grabs her shoulder and turns her around.  He tells her about Tails and begs her to stay.  In tears, Amy changes her mind on the spot and agrees.

The player is now at the final boss.  Robotnik's machine is in a new super duper mode, but now it's careening out of control.  Robotnik is detached in his eggmobile while Sonic tries to subdue the machine.  Because of Sonic's final blow, the machine begins to fall forward, but Sonic becomes trapped by the torn-up metal floor and can't get away.  Time slows as Sonic's life flashes before his eyes in the form of many clips from previous games, recreated in FMV.  Tails's image becomes more and more prominent, and at the last moment, Robotnik kamikazes his eggmobile into the front of the falling machine, sending Sonic careening free.  Robotnik perishes.

After a while, the planet returns to normal and Sonic keeps on running, and keeps on running through the credits at the bottom of the screen.  I realize the plot is really dark compared to what a usual Sonic game would be.  It was kind of an accident.  I also realize there are many plot holes, and lots of room to develop Robotnik's character.  What would you add, and how would you change things to maybe be less dark and more uplifting?

P.S.  The reason I didn't allow Sonic and Amy to end up together is that in all the games, Sonic has had zero interest in her, if I'm not mistaken.  Giving him sudden interest after Amy completes an act of heroism feels unnatural.  They likely just have no chemistry.  But you can debate this, in fact I welcome any alternate ideas.