[Sims Katie]

That's also possible, scary.

Another idea is that his creator isn't unkind but simply outgrew imaginary friends and doesn't think about him. Wilt's been at Foster's for almost 20 years, so whoever imagined him would be an adult now. Imaginary friends would be the last thing on their mind (Look at Imaginary Man and Nemesister. Their creators did come back, but not until they were already grown up with children of their own, and only because they heard about the friends again)