The (More Than) Complete Cast of CVRPG
Heroes, Villains, Low-lives, and Agents of Leisure
Mrs. Claus (Don't Call Her "Princess")
Although the concept of "Mrs. Claus" hasn't existed for anywhere near as long as the original Ol' Saint Nick, she's taken a quick and permanent hold in the minds of believers (kids, immature adults, hipsters). And when it comes to belief, once an idea is set, it's not going anywhere.
Not that it doesn't make a certain amount of sense for Santa to have a companion. He spends all year up north with the elves (who look like little kids, so finding "companionship" with them is just creepy). When he's off on adventures or delivering presents, someone has to be at the North Pole, taking care of business. It's just logical for Santa to have a soul-mate, someone that lives with him and helps him and shares equally in the business of Christmastime.
The fact that Mrs. Claus looks a lot like a certain adopted royal (Princess Isabella) speaks more to who her husband is than anything else. More than likely if Santa were someone else, someone gay, "Mrs" Claus would be a dude. We're just saying that personifications are influenced by the people around them.
Just because she's tied to Santa, Mrs. Claus is still her own person. Presumably if someone else were to become Santa, the current Mrs. Claus would move on, find a new life, and someone else would assume the "Mrs." title. She doesn't cease to exist, she just finds someone else to do with her time.
This Mrs. Claus is a fiery warrior, though, so it's hard to say if she even needs a Santa around to run the north. She might just have this whole "Santa" thing down better than her husband...