Dark Elves: "Azura, Boethia, Mephala! Save your loyal servants from destruction"
Daedric Princes: "After all the time we put into setting this chain of highly amusing catastrophe up, you think you can change our minds? Its much more amusing to watch you all burn - oh look! I think your sister just caught fire!" (Cue laughter of amusemant from the Daedric Princes)
Yes, they deserved it, because they were asking for it. If you don't want to get kicked in the groin, don't go up to the God of Groin-kicking and offer to serve them and expect them to need you for anything but a practice target for their boot.
Not really. When they Dunmer were still the Chimer (i.e. when they still followed Boethiah, Mephala, and Azura) the lessons their gods taught them did nothing short of keeping them alive. The real reason they got screwed over is because of The Tribunal, if the Tribunal never existed, neither would Dagoth Ur or the need for the Nerevarine. I suppose the blame for The Red Year really falls on Vivec more than Amalexia or Sotha Sil.