They need to fix it in a few places.
First, Google+ should not delete albums or photos from blogspot, just hide them from your profile.
Second, Blogspot needs a recycle bin, giving you a grace period to change your mind. You can always allow people to permanently delete items from the recycle bin for when you really need to completely delete something with immediate effect.
Third, the blogger export blog feature should include an option that also backs up your images for you (at the very least the ones hosted on Blogspot or Picassa).
As for getting our images back, a reply on the G+ forums indicates that Google are not able/willing to do this for us.