There is no evidence any retired characters will be returning The Simpsons at least in any recurring capacity that they require new voice actors.
Edna Krabappel died off screen during Season 26.
There's no reason to believe Dr. Marvin Monroe will be returning if doing his voice caused suffering for Harry Shearer.
There's also no reason to believe Capital City Goofball will return. He was a one shot character who served no real purpose to the show so there's simply no logical reason they'd bring him back.
Finally Troy McClure, after Phil Hartman's death, out of respect they retired his character. They aren't going to revive him.
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There are no Arabian characters on The Simpsons.
There are two websites that you can visit to create a Simpsons characters, see the links below.
Matt Groening created them and he & producer James L. Brooks turned Matt's characters into a series.
Rob Van Dam is a retired professional wrestler best known for his stint in WWE and ECW. He is currently retired and pursuing movie and TV program productions. As of now he is not planned to return to the WWE.
All of the characters (except God & Jesus) have three fingers & a thumb.