What evidence do you have of "demand falling off a cliff"? Gatwick has just had it's busiest (in terms of flights and departing passenger numbers) Tuesday, Wednesday, Thursday and Friday since February 2020, despite "current news" and "new restrictions". Even busier than a fairly restriction free October half term. Red list aside, long haul loads have been barely affected by any changes recently.
But how is that specifically relevant to TUI? Aside from Morocco, Goa and a few ski flights, some of which are being re-routed, TUI are operating to more or less everywhere they would be at this time of year.