I hope not, but I did come up with three ideas when answering "How would you end the Simpsons?" questions.
The episode begins with Lisa in the attic opening a hidden door to a tiny room (where she has secretly being keeping the petri dish from "The Genesis Tub")
She arrives just in time to see a rat moving to attack her creation, after chasing the rat away she speaks with her tiny people and they decide to use the Rebigulator to increase the size of the Petri dish world.
Meanwhile: Marge and Maggie set off to do some errands in Shelbyville.
Lisa carefully packs the tiny civilisation and a remote to the Rebigulator into a specially designed bag, and sets off to find a safe place to grow Petri dish.
(Some stuff happens)
The Petri dish is now falling towards the Earth closely followed by Lisa. Lisa presses the remote and the Petri dish starts to grow, Lisa lands safely in the still falling civilisation and the now giant Petri dish crushes Springfield.
Marge and Maggie return to find Lisa's civilisation where Springfield once stood and are escorted to Lisa's throne room, there they find Lisa sitting on her throne.
(Hugging and such).
[The end credits]
The episode begins with Professor Frink discovering that one of his experiments is still running, so he turns it off.
Over the course of the episode the people of Springfield experience accelerated aging as their bodies catch up to their true ages.
The episode ends with Springfield devastated and most of the towns people dead.
A man enters the world of The Simpsons in a desperate bid to end the series.
He does this by trying to assassinate the Simpsons family.
He obviously fails and by the end of the episode he realises that he is now stuck there forever.
It would start in the real world, in a science lab.