Just to note - Air India’s STN-BOM route was specifically launched as a temporary solution at very short notice. It allowed them an immediate start before their additional LHR slots became available in the summer, following the earlier collapse of Jet Airways. Of course, what was to be a few months sadly became only a few weeks due to Covid.
Thought this worth pointing out, as it was not a spoiler for prospective Indigo intentions and neither was it an example of ‘failure’ of STN re long-haul.