What if Chet got to keep the Turtles?
 

Basically, what would have happened if he didn't drop them into the sewer?

The Foot crime wave would have overrun the city and Shredder would have no need to build Krang a body or even bring Krang's soldiers from Dimension X.

Then we would just get “Elderly Mutant Ninja Rat”

Not really, in Mirage, Fred Wolf, Archie, 1990 (I'm just going to assume Chet existed here) and 4Kids, Splinter only got into contact with the Ooze because he wanted to clean it off the Turtles.

Well, I suppose, realistically, the story would never happen, and then we would never hear about it.

But, let's be honest: If Chet kept the turtles, then he would go home, and then inexpicably the Foot or The Utroms or the Triceratons or SOMEBODY would track him down, a bunch of stuff would happen, and then the turtles and Splinter would get made anyways, or Chet would be the "Splinter" or even the April of this timeline. Ultimately the net result would be something very similar to what already exists.

That's the problem I've always had with most "What If?" stories in any medium is that very rarely do we get a true what if. It always feels like the writers copped out, because What If? stories can be broken down into two basic categories:

"What if one day someone left the cheese off of Mikey's hamburger?

1. The exact same thing ends up happening anyways and Mikey still has cheese on his hamburger by the end of the story.
2. Everyone dies.


So if Chet keeps the turtles, either they still become the turtles, or Shredder shows up and kills everyone.

At least in the cartoon, Splinter would have still mutated, depending on how long the chemical is active after it's been exposed to the air. Shredder randomly dumped it in the sewer hoping it would kill him or something, while he was out. I'd imagine Yoshi would have come home and thought 'aw man, what the hell is all this mess?' and possibly would have come in contact with it upon mopping it up. Unless of course, he had the common sense to not the mysterious glowing pink liquid directly and wash it out with a hose or something.

That guy would’ve been splattered by the truck! That’s all I know would’ve happened!