That was in the episode "La Cage Aux Mikey", and Mikey's parents didn't change their minds; they wanted to visit their son in Japan, but they weren't able to because a killer bee invasion closed all of the airports in Ohio. The invasion was later quelled by Ozu's weather machine (which was the B plot of that episode).
In any case, I fail to see how simply not being home when Mikey calls them makes Mr. and Mrs. Simon bad parents. Mikey doesn't live with them anymore, so it's not like they have to sit by the phone all day waiting for him to call. Parents have lives too, you know.