[quote=Gowi]
How upgraded is his equipment that he uses? I mean if I want him to survive I usually send him as an escort or use him as an additional squadmate.
[/quote]

His equipment is fine but I'm pretty sure that's not the issue. It's one of those 'you made the wrong choice' things I think because I don't use him in the fight at all. After killing the the reaper I'm just treated to a cut scene of him dead on the ground even though he was fine just a minute ago.