Doesn't NWI close at night whereas STN is H24? Might get in okay but what about carrying on to Paris when fixed. Also routing takes that flight much closer to STN than NWI. If a serious problem what flights could you put the pax on from NWI? STN seems a good call to me (purely from a logistical viewpoint).
Luckily I am not a cynic but if I were I might think STN a good choice for a crew to go out of hours and fly home, more so than NWI!