Not true, flights didn’t restart from EDI, ABZ, NWI or BFS. Albeit, the latter three are normally only summer bases but ABZ and NWI do have occasional flights in winter, not too many fewer than LTN which has hardly even been a base in winter in recent years.
To clarify, LTN was the only year round fully crewed UK base that did not re-start in July.......EDI, ABZ, NWI and BFS are all normally operated by seconded Sunwing aircraft in the Summer (but with Covid this clearly was not going to happen anyway!)
Management are denying a full base closure is on the cards but in reality anything is possible! The decline in TUI ops at LTN seemed to coincide with reports of many passengers complaining about the poor terminal experience a few years back when there was also huge queues of cars trying to access the drop off area. Since then, TUI have constantly increased the number of holidays using EZY from LTN (which seems now to be the preferred option)