We see that Kaeloo's future self is a cold-hearted, money-hungry businesswoman. Think of the state Kaeloo's life is in before she resets the timeline: Stumpy has developed some kind of anxiety disorder, Quack Quack has become embittered with life, and Mr. Cat abandoned the rest of the main four for money. These were most likely the circumstances that drove her to become that way in the future.
Mr. Cat has to leave Smileyland to spend his lottery winnings because, as mentioned in Episode 49 and Episode 193, Smileyland doesn't use real money.
Kaeloo and Stumpy's future selves are shown living in Smileyland; when Stumpy re-wrote the universe in Episode 105, he probably got rid of the "no adults" rule from Episode 34 so he and the others could stay together forever.
Mr. Cat cares even more about money than he does about Kaeloo. And given the kind of devotion he shows Kaeloo and the crazy things he's willing to do for her sake, one can only imagine the kind of things he'd do for something he cares about even more than her...
In "Let's Play Grown-Ups", before the timeline is reset, Bad Kaeloo's future self doesn't seem to remember who Mr. Cat is. What if something similar to this episode ended up happening in that timeline as well?
In the present day, Mr. Cat is the glue that holds Kaeloo together with Stumpy and Quack Quack. Every time Kaeloo inadvertently ruins her friendship with the others, Mr. Cat is the one who fixes it for her. If Mr. Cat were to just abandon the main four, Kaeloo could permanently lose Stumpy and Quack Quack, while still suffering from the loss of Mr. Cat.
