Depends on how creative you get. Perhaps John and Elly decided that Mike came along before they were ready to have kids and put him up for adoption instead of sticking him in a bureau drawer. Liz would be stuck, but have things a bit easier without having someone who competes with her for attention. And John can be killed off as soon as April is conceived -- Elly can flail and look for someone to take Liz while she's grieving, letting the kid be raised by her long-lost uncle from Greenpeace.