@Connman234 Loyalty isn't the only thing that matters for keeping your squad alive during the suicide mission. You also need to choose the right people for the right jobs. See the flowchart for more information.
To summarize the last part of the flowchart: The most confusing part of the suicide mission is the ending. Ideally you don't pick the best defenders to go fight the boss with you, and Grunt, Garrus, and Zaeed are the best ones. If you want to play it safe, you bring two weak defenders to the boss, like Jack and Tali.
In my very first playthrough back in 2010, I made Zaeed the crew escort and took Garrus (and I don't know who else) to the boss. I didn't leave enough good defenders behind, and in my case Mordin died because he's the first to go.
Thought it is kinda strange that in your case Legion died, since he's supposed to be one of the later ones to go. Did only one character die in this scenario?
