Window of opportunity
How long was the window of opportunity for Esther to go missing? According to Dan she contacted him at 16:00 on the 22nd Nov from the pic de Sauvegarde, if we ignore the issue of when the photo he received was taken for the moment, she had, according to a named witness, Marti Vigo del Arco, passed him at around 15:00 so it is not unreasonable to believe she was at the pic. Dan states that her plan was to spend the night in the refuge de Venasque (the BBC reports that this last contact was from the pic and separately actually from the refuge, I think that’s just more poor reporting, you would think that they’d notice they have reported contradictory things!). Looking at hiking plans etc it is 1.5 hours from the refuge to the pic so I figure that it is at most 1.5 hours from the pic back to the refuge (downhill).
There is no sign that she was at the refuge, if she was there she should have signed in (and actually paid) “Un cahier des présences dans le refuge d’hiver est à compléter lors de votre arrivée.” (taken from the refuge de venasque site).
We also have plenty of reports suggesting that she was an experienced hiker, self confident, responsible and intelligent so given Dan says she was going to the refuge that’s exactly what she should have done, no deviations, etc, It would have been dark by 17:30 so no time to be doing other things anyway. Following on from this she should therefore, if she got there, signed in. An experienced and intelligent hiker would also know that in the event of something happening to them this would leave some sort of trail.
This leads me to suggest that there is only 90 mins for whatever happened to her to take place.
On that basis it seems very unlikely that a third party was involved in some sort of foul play. The hikers she met on the way did not report they had seen anyone else up there, they haven’t reported that someone else passed them in the same direction as the pic. In addition they have then got to do their foul deed, cleanup and hide any and all evidence and not be seen coming down themselves. There can’t have been many people that even knew she’d be up there so unless she just happened across someone prepared to commit serious crime (and then again, cleanup and hide all evidence) without any motive I can’t see a third party being involved. They would have to have means, motive and opportunity.
That leaves Esther coming to some other mishap but only on the trek from the pic to the refuge, thus a relatively small area to search and still no sign of her.
If on the other hand we say that Esther was not following what we believe to be her plan and did something (went somewhere) diametrically opposed to what she said then she would be harder to find given that she had a couple of days to do it. This is turn would lead me to think that Dan didn’t know her as well as he suggests which after all that time together would be very odd indeed.