That's not it Andy, I have no doubt they may of done that, and that she may be dead in that scene. That scene just involves a lot of them dying which seems odd is all. If we got dev confirmation she was dead then yeah. The dev said don't assume anything and it would 'make sense in context we don't have'. None of that's confirmation, but like I said she could be dead, all 3 could be. From the way that scene plays out Sera and Leliana are likely kapoot, or at least Leliana (has a weapon to her throat).
It's also likely Sera is just knocked out, and as you leave Iron Bull rushes in and fucks **** up saving the 2, and when you 'come back from the rift' you find your group, not dead, but pretty screwed up and morally shaken. It's a BioWare game, it literally can go either way and that's ultimately all im saying.
Also that person saying it wouldn't stop the argument is true, people are crazy and they'll argue over anything even with evidence to the contrary. They'd just say they're trying to trick us to justify there position.
I guess the point i've failed to get across - stop assuming stuff. Maybe it's that way, maybe it isn't, no reason to just up and decide that's exactly how it is and argue your uninformed position like a mad man =P