1. So the owner of the building found Madeleine dead in the lift and decided to dispose of her body?
2. She woke and wandered and was murdered by a drunk driver who disposed of her body?
3. Madeleine fell down a man hole and the contractor was in the vicinity and happened to find her and dispose of her body?
4. Madeleine went to meet the abductors?
5. She drowned in the pool and the owner of the pool felt liable and decided to dispose of her body?
6. Wouldn't Kate or Gerry have observed a dead Madeleine if their daughter had choke to death when they went into the apartment? Nor is it exactly waking and wandering.
7. Just assuming the owners of the inadequate rail were hanging around the tapas between 9 and 10 o'clock, did they discover her dead and decide to dispose of her body?
These are just some of the possible eventualities that could have been the fate of Madeleine.
As you pointed out: "6. Wouldn't Kate or Gerry have observed a dead Madeleine if their daughter had choke to death when they went into the apartment? Nor is it exactly waking and wandering."
OK choking could occur outside as well as inside the apartment. Woke wander, choke, taken to doctors, recovered, person changed their mind and abducted her.
As you pointed out: "7. Just assuming the owners of the inadequate rail were hanging around the tapas between 9 and 10 o'clock, did they discover her dead and decide to dispose of her body?"
That is possible, they may have been out walking and returned home. Nothing unusual about that.