It was not aer europas decision to pull out of BLK but the tour operator, and the reasons for this stretch far beyond the fact Jet2 appeared on TFS, more to do with operational logistics and costs.
Why would Monarch pull out? If you look at where they operate, Manchester for example, they compete with Jet2, GB Airways, BmiBaby, Thomsonfly plus the charter ops of TCX, MYT, FCA etc etc etc.
Jet2 and Monarch are also very different carriers, and offer very different services and appeal to different markets, they complement each other very well.
In 2004, 205k passengers from BLK's catchment flew to Malaga, I am sure the airport can sustain 9 -10 flights per week.
There are no monarch services from any airport bookable beyond march so I rather feel that statement is void.
I do not know what Monarch's intentions are, but I would hazard a guess that they will operate the route - after all, why wouldn't they?