They walk outside and see a scorched landscape with ruined planes and dead whales and shit. The vault they showed, while large, didn't show off the capacity to be a long term living option.
I had to look it up - movie pegged the main impacting comet fragment at 9 miles across. So smaller than Chixilub by around half, but still fucking huge.
Chixilub was a double whammy because the area it impacted as very sulfur rich, so not only did you get a massive cooling event, but also acid rain from hell. So assuming Europe isn't very sulfur rich, then maybe the same shit doesn't happen to the same degree, but it would still wipe out civilization. You'd still have a cooling event due to all the ejected material + all that material would rain down on the planet and cause secondary impacts + the ultra shockwave.