It is an interesting question.
I'm not sure that the progress of the investigation would have been much different whether the McCanns had been in Portugal or England.
But there may be some nuance I've missed ...
As far as the progress of the investigation into Madeleine’s disappearance is concerned, I don’t think there would have been much difference, too many elementary mistakes had been made for any more progress towards finding her to be made.
As far as the investigation into Madeleine’s parents is concerned … I do not think that would have happened.
The ‘honour’ of the PJ would not have been allegedly impugned.
The dogs would not have been brought in and allegedly alerted.
The hire car would not have been hired.
The second mistaken Smith sighting would not have occurred.
The previous three statements would have meant that the McCanns would not have been made arguidos.
It is possible Dr Amaral might not have been removed from the case when he was and he would not have written his book or made his documentary.
… and no-one would be trying to find out what happened to Madeleine now.