NCL diversion to LHR
Diverting the flight back to LHR might not have been such a bad move. It could have allowed the option of a quick fuel-and-go as soon as NCL reopened. And I imagine BA would have wanted their aircraft and crew to be in place at NCL for the following day’s operation.
Organising an unexpected coaching operation late in the evening is not necessarily as quick and easy as one might think.
The real test of course is what actually happened to the passengers. Did they get to NCL that night or did they have to overnight in London and was the following day's NCL departure affected ?