You can take it with the pinch of salt it deserves but “dozens” is probably fair for someone in that position. I mean, realistic talks would be much narrower and successful ones narrower still, but I could list probably 30 airlines that ‘could’ fly from SEN*.
Here’s some examples that are outside the box, not particularly likely but not beyond complete fantasy either: BA Citiflyer weekend operation, Eastern to Newquay, Transavia to Amsterdam, Loganair to Newquay, Vueling to Barcelona, Volotea to somewhere like Genoa or Catania, return of Blue Islands, return of Air Malta. That’s 8 already
*Subject to Covid, slot constraints elsewhere, routes dropped by others across London, Brexit