There are so many potential factors such as:-
The geopolitical situation in the Middle East, the fall in the value of sterling principally precipitated by the Brexit vote, and too many seats seeking too few passengers - probably also because there is a finite amount of accommodation in the Med. resorts, that means that there is an imbalance between seats available and beds.
Aside of that there always the potential for allegations of poor management, and there will undoubtedly be severe criticism of Greybull Capital who will again not come out of this smelling of roses - they do have previous in other sectors.
How much of the slack (if slack there is) will be taken up is questionable. The industry might be better restricting capacity and raising yields, but there's always one that will break (unofficial) ranks and I suspect one or the other company will use Monarch's demise as an opportunity to buy market share.