Well, looking at Stoke's point tally, that wasn't really affected all that much. Went from 46 down to 45 in the season they played in Europe, and then they placed higher the next season despite having 42. The placings are really all about the rest of the teams in the league I'd say.
Meanwhile, with Swansea, you could say that there were other factors - I'm pretty sure by that point Laudrup had worn out his welcome by talking himself up about a bigger job; and also, looking at Wikipedia, he appeared to have been sacked by Swansea because of a poor stretch of two months or so from February 4 backwards, which probably stretches back only to their final group stage game.
I don't think there's anything too conclusive you can gain from those two cases.