Unless, somehow, they have it protected with another person.
Which I don't believe to be true at all. I agree with you and think the baby is dead. They know they'll be charged for that too but I am surprised one of them hasn't broken yet - so there is still a possibility.
A lot of folk have said that at each location they have been they have been staying with friends etc. Which realistically is ridiculous. One of the friends would have likely talked and there would have been zero reason to buy a blue tent from Argos (To lug around with a new born baby - smart idea that, lets stay with friends or rent a house but carry an Argos tent around with us too - If they didn't need it they would have ditched it. They would have likely been following the news too and know they have been on CCTV with it).
Saying that they would likely leave the baby with somebody safe also IMO doesn't make sense, actually, it does from a logical approach but both MG and CM are hardly that and have without a doubt endangered the newborns life as soon as it ended up in the car when it was born.
A medical procedure has taken place, it is highly advisable to get checked out not only for the mother and child. Even if the child is alive god knows what kind of illnesses or diseases it could have potentially already have 54 days in to its life.
So much has been overlooked simply by saying "Maybe they want to be good parents and be left alone" Sure, keep telling yourself that!
If they find the baby alive they can charge them for neglecting it for the last 20 hours or so its been hidden!