Without being fully in the know, its impossible to predict what TUI's intentions are when it comes to LTN. Bear in mind that LTN was the only UK TUI base which did not re-start flying in July and pre-Covid only 1 x 737-800 was due to based at LTN this Summer anyway!
Ironically, the first TUI passenger flight since the March shutdown departed this morning with G-FDZD operating to ACE