Okay, fine then. Here's the first part of my version:
One day, in the late summer of 1982 (or 1983), Justin comes to the Fitzgibbons' farm to search for the Brisbys. Failing to find them in their block, he comes across Breta, who leads him to the Brisbys.
Meanwhile, in the city, we introduce Racso, possibly during a scene where he's stealing food or something. Racso is established as a playboy. He and his mother live in the city.
Racso was born by accident after a sex innuendo between Jenner and whoever Racso's mother is. Jenner hated Racso and wanted to kill him ever since he was born, but the mother wouldn't allow it. She and Racso left the rosebush shortly after that (This allows for Jenner's death AND the existence of Racso). Racso eventually decides that he wants to see the Rats of NIMH again (Maybe because he hears they're opening a school, maybe because he wants to see his father), and he sneaks away.
Meanwhile, in their summer home inside a tree trunk, the Brisbys (Mrs. Brisby, Teresa, Martin, Timothy, and Cynthia) are having a typical morning, when Breta and Justin arrive. Justin tells the Brisbys that the Rats of NIMH are building a village in Thorn Valley, as well as a school. They want little Timothy to join. The other children are invited as well, if they want to help out.
Justin confides privately with Mrs. Brisby that Thorn Valley and the surrounding area is in potential danger, and that the real reason he came was to warn her and ask for her help (since she's the only mouse they know and can trust; her small size could be used to an advantage). Mrs. Brisby agrees to help the Rats of NIMH.
Jeremy is shown as the head of a family. He's still with Miss Right (Who knows what we'll name her?), and they have a son.
Racso comes to the Fitzgibbons' farm, searching the rosebush the Rats used to live in for an opening. (Unbeknownst to Racso, this is actually a different rosebush; the first one got bulldozed away) Jeremy arrives, attempts to help Racso get in, and gets hurt in the process. A yelp of pain from Jeremy wakes up Dragon the Cat, and Dragon attacks. Jeremy saves Racso, and after a conversation, Racso finds out the Rats of NIMH are in Thorn Valley. Racso offers a candy bar to Jeremy, but for some reason he only takes the foil wrapper.
Jeremy comes to the Brisbys and they're ready to leave. They climb onto Jeremy like so:
During the flight to Thorn Valley, at the break of night, a hawk attacks. Timothy is wounded and falls off. After losing the hawk and failing to find Timothy in the darkness of night, the Brisbys continue to Thorn Valley.
Timothy comes back around, and finds he's being taken care of by Racso.
Jeremy and the Brisbys arrive at Thorn Valley (which, BTW, gets a big, dramatic reveal and will not be anywhere NEAR as sophisticated as in Timmy to the Rescue) and inform Justin that Timmy is gone. Justin assembles two search parties (One for him and one for Mrs. Brisby) to search for him. (Brutus doesn't talk and he still has no pupils)
Mrs. Brisby's team finds a bonfire in the middle of the forest (courtesy of Racso). There's an action scene here to put it out.
Justin's team finds Racso and Timothy. They bring them to Thorn Valley.
Timothy is taken to the infirmary, and the Brisbys are given housing. Later, a village-wide meeting is held, where Justin explains the danger to Thorn Valley. He subsequently introduces Racso and calls for Racso's father/someone to lodge him. Nobody claims Racso/Nobody will lodge Racso, so Mrs. Brisby allows him to live with them.
Racso and Mrs. Brisby go the infirmary (meeting Isabella on the way), and see Timothy all healed up. They take them to their Thorn Valley house, and the next day, they all do their part for Thorn Valley.
The next day, Timothy and Racso start school, Cynthia goes to a nursery, Teresa helps Isabella in the kitchen, and Martin is stuck working in the gardens, with a nasty rat named Bertha bossing him around. ("She makes the Shrew look like an angel!" he would say about it)
That's all I'll share for now. There's more, but I don't think it'll be any good.