I lost Mordin and Zaeed (I had no idea until last week). Just went through the final mission again, then did Shadow Broker.
Guides break down how to simple it is to keep everyone alive. It comes down to a characters 'rating', which is a fixed number, and who is in your squad. So Mordin is a very weak character while Garrus is one of the bottom three. By taking Garrus and another strong character last time, the rating for the rest of the crew dropped to where not everyone would survive. In the end I just brought the two weakest characters with me into battle and everyone made it out alright.
Since I didn't get the Kasumi, Overlord, or Arrival DLC, I'm just going to use the PC save file editor to make it seem like Kasumi was in my game, loyal, and survived. Don't know how the Arrival DLC stuff will be handled, if there were any important choices. Shadow Broker seemed pretty important.