Why does dafhne in scooby doo mystery incorated diced to not come back rejoin the gang episode 27?

You're likely thinking of Daphne Blake from the classic "Scooby-Doo, Where Are You!" series, not "Dafhne". There is no episode where Daphne leaves the gang permanently, and she definitely doesn't rejoin them in episode 27.

Daphne is a core member of Mystery Inc. throughout the entire classic series and most subsequent iterations of Scooby-Doo. She consistently helps solve mysteries with Scooby, Shaggy, Fred, and Velma.

There are episodes where Daphne may be temporarily separated from the group, but she always rejoins them.

Perhaps you're thinking of a specific episode or a fan-made story?