The fact that you loved their dog and that you understand how much their dog was such a big part of their life and their family makes you the ideal person to call them. It was so helpful when my dogs passed to be able to speak abouth them and my pain to people who really cared. It is one of the most caring things that my friends have done for me. I really needed to talk. Presuming your friends feel the same way, call them and give them the opportunity to talk about what happened, etc.