Melissa and Chris do not appear in The Sims 2, and what happened to them is not mentioned. In "The Sims 2: H&M Fashion Stuff two Sims that looked like Melissa and Chris appeared in a preview wearing the clothes they wore in The Sims (console) version, but it is not confirmed that they are really Chris and Melissa. If they are, that was the last time they were shown to the public.