Wow -- you gave them 1000 and they didn't even use it for the wedding? That is very upsetting. Unfortunately, the process of planning a DW has also tested some of my own friendships. Some people do not know how to handle situations like this, and don't understand that honesty works best. I had a friend tell me she and her husband could not afford to come on the trip, and it was devastating for her to have to tell me, she could not belive she had to miss my wedding etc., then I found out she booked a trip to Mexico with another couple -- I was speechless and we have not talked since. I sent her a not so nice email (immature on my part, I know - but I was caught up in the moment) and expect that to be the end of of our "friendship"
I believe you have done all you can do in your situation, now you just have to focus on those who WILL be there to make your day wonderful!