In the beginning when Chuckie and Tommy are put to bed by Stu he says "goodnight Chuckie, your mom and dad will pick you up in the morning"
Was it realized when the series first started that Chuckie's mom was deceased?
The original writers never intended for her to be deceased. They created Chuckie before the parents, then created Chaz, and then decided Chaz is a single dad, but couldn't decide what happened to the mom. The thought was they were divorced because she didn't want to put up with him, but they didn't want to write her as divorced because that would open up a can of worms with the Nickelodeon brass.
The new writing staff wrote her as deceased.