I'm not sure how long the A330's will last but What I do remember is that they were apparently looking for some new long haul aircraft, so I presume they will go around then.
I wouldn't be surprised if Monarch quit Long Haul ops...
With the tour operators doing nearly all their operations in-house now, there seems to be little need for an airline like Monarch to offer their A330's for charters.
We have seen the A330's used more and more on flights to Egypt and Canaries in the last year or two, and going back 5-10 years ago, these aircraft were maxxed out flying long haul routes, and even had to supplement the fleet with a DC-10 and 767 for several summers.
While I am sure the airline operates the aircraft profitiably, does it really make sense going forward to operate a small sub-fleet of 2-4 aircraft... Especially if the airline wants to focus on LCC routes within Europe and North Africa.
I do sometimes wonder, if the airline did order some wide bodied aircraft, if they could possibly go down the path similar to Norwegian, and start flying Low Cost Long Haul routes. But this is high risk and Monarch are usually quite a conservative airline.
If the airline did want to get rid of their A330's soon, I am sure Air Transat would jump on them in a shot! They are after second hand A330's to replace the A310's and grow the fleet too.