There is high demand for charter airlines especially due to the loss of Thomas Cook. Freebird that would normally be used by TUI for non based Turkey flights will also be operating dedicated charters for On the beach who used to use Thomas Cook so will have less availability to operate flights for TUI.I don't believe for there is no airline that would take up a TUI route. For a starter a airline doing a TUI route is good business and I would think better work than they could get else where. The only thing TUI would have to be carefull with is the quality and operations of any foreign airline as a few out there is a bit suspect,but saying that there is a lot of good airlines out there as well. I should say if a route is dropped then it would be down to pax take up,also there is many other things that dictate weather a route is taken up or not.