Can't see it making much of a change. BD get a good load on the ORD flight, loads from LHR are by no means guaranteed so would they be mad enough to damage their business by pulling it?
Although with BD you can never tell...
As for Vegas and the fleshpots, Virgin Holidays take a lot of the seats for their Manchester clients. VS might consider it worth their while to ship a crate north and take those routes over if BD want to withdraw. Holiday departures are much more sensitive to origin than business travellers after all, passengers off on their fortnight in the sun don't want to be transiting at Gatwick or Heathrow if they live in Bramhall.
It depends on whether BD can arrange extra lift in the short term, and whether they want to retain their MAN operation as a second string.