Mrs. Quagmire appears in three episodes of the first two seasons. Her last appearance is in "The Lottery", where she finds and redeems Kel's winning 64 million-dollar lottery ticket. She probably moved to a different neighborhood.
In "The Contest", Kenan tells Kel that when he clapped for what he heard on the radio, he was clapping for Michael Jordan (he was listening to the Bulls game). Kel gets excited that Michael Jordan is, to his knowledge, in the store somewhere. Sharla sarcastically tells him that "He's right there under the table next to Shaquille O'Neal." Kel doesn't believe her, possibly because it would be at least somewhat plausible for Jordan to be there, since he plays for the Chicago Bulls, where the show takes place. O'Neal, meanwhile, played for Los Angeles Lakers at the time, so there'd be no logical reason for him to be in Chicago during the NBA season (unless, that day, they happened to be playing their one game a year in Chicago, which is possible but unlikely).
In the episode "Mo Sweater Blues", Kyra and Kel react similarly when the waiter at a Chinese restaurant recommends a pu pu platter. Kyra exclaims "Ew!" while Kel says "Man, I don't want any pu pu!", and Kenan has to tell both of them to be quiet. That's why Kyra likes Kel so much— she likes older boys (which we find out in "Mental Kel-epathy"), and unlike most other older boys, Kel's intelligence/maturity is actually on her level.
Kenan ditches work in the episode "Skunkator vs. Mothman" so he can go with Kel to a comic-book convention and find a rare comic to complete his collection. It ends up being a lot more trouble than it might have been worth (as usual), and it seems like he could have just told Kel to pick up the comic for him. Kenan might just be smart enough to know, however, that a plan along those lines is doomed to fail because Kel is so absent-minded, so he didn't even entertain the notion.
The episode "Pair-Rental Guidance" sees Kenan attempting to hire actors to pose as his parents and attend a meeting with his principal, so Roger and Cheryl don't find out that he's in trouble. Kel is tasked with gathering potential men and women to play the parts, and the first couple he presents to Kenan are French and speak no English. So how did Kel even explain the situation to them? During the opening of another episode, Kel shows off his linguistic skills by introducing himself and Kenan in French, implying that he has at least somewhat of a grasp on the language.
At the end of the series finale, "Two Heads Are Better Than None", the Headless Knight's body is shown hanging onto the car of the middle-aged couple Shelly and Shelly Wilson, who helped Kenan and Kel escape. Did it kill them?
Considering that the Wilsons proved themselves to be surprisingly tough when delivering a No-Holds-Barred Beatdown to the Headless Knight's servants (especially since Mrs. Wilson was in a leg cast at the time!), they'll probably be just fine.
