I'm sure the club were planning for the succession in the full knowledge that Mourinho was a very remote possibility anyway. Pellegrini seems to have gone off the radar, so on the face of things it seems it's either Koeman or De Boer.
Would prefer Koeman in that scenario due to his experience. De Boer announcing he was going to Valencia or elsewhere next week would really set the cat amongst the pigeons, and increase the pressure on Moshiri to get Koeman IMO as his preferred option. AC Milan now likely to be looking for a new coach too (Rudi Garcia now being linked there).
If there is a "3rd" option (discounting Pellegrini) being considered would obviously love to know who that is. I would imagine now that things have crystallised as far as the boards thinking is concerned and a lot of names have been ruled out. They must be down to the final 2-4 candidates you would hope. Perhaps Esk will have an update by next weekend.
The unknown is intriguing and exciting - particularly the prospect of someone making a late challenge to get the job who wouldn't have been touted initially (aside from the likes of O'Neill, Hughes, Howe and their ilk). I hope the search firm have earned the money being paid to them, I wouldn't think much of them if they presented a list of possibilities without Unai Emery on it.
Hope that things get sorted in the next fortnight. There is a lot of work to be done.