The board, I would suspect, are buying time at this point to get all their ducks in a row. Compensation agreement needs to be reached, which should be simple, an interim replacement needs to be appointed, and a permanent replacement needs to be agreed upon. I would suspect that the latter two points are a bit of a problem, as it would appear the desire is Zidane but the club is some way away from convincing him to take over. The public will be the last to know, but I am sure that Solksjaer has already been told that he will be removed from his position pending a formal announcement.
The interim appointment will certainly come from within, with a view to having a permanent manager in place within a week to ten days. Whether that permanent manager takes over immediately, or in the summer is open to speculation; but I would expect Phelan to probably be in charge for the next match, as the most experienced of all the coaching staff. One would expect that the new manager will bring in all his own coaching staff. I could easily see Phelan remaining in some capacity, as he has the historical credentials and knowledge of the club, and I wouldn't be surprised if McKenna remains in some capacity, as part of a larger more experienced team. He was highly rated when we poached him from Tottenham, and too much is made of his performance as a coach when the buck has to stop with the manager.
We shall see.