Zoarath
Nail, head, miss! In-house airlines provide a majority percentage of a tour group's lift, getting their customers to their holidays. Changing TCX for a newer model doesn't alter the fact that due to rubbish commercial decisions by the tour operator, less lift is now required - hence a smaller airline. The locos probably wouldn't end up wanting too much of their summer capacity taken up with other people's passengers because the work is so seasonal and makes the retention of the aircraft and crews over the winter a major headache.
For tour companies that wish to keep control of their product from booking until the customer walks out of the arrival terminal at their home airport there is no better way to go than your own airline. You only need to look at the furore surrounding the recent "Monarch" incident and subsequent bad press to see that flagging out if not done carefully can lead to worse publicity as it is seen as endangering people to save cost whether such criticism is justified or not.
You'd be better drawing parallels between MYT and the current mess at TCX by considering how the banks did the same recapitalisation with MYT as they are now and look how that ended. Where is the large tour operator to buy the remnants of TCX? TUI probably wouldn't touch it with a barge pole - not enough margin for them.