Actually we are not implying she literally died during Going Under 'cause it's pretty clear she survived it and oh well she wasn't that bad right after it.
In all honesty while I do think that Eric Delko died (figuratively) during "Man Down" ( I so wish he would have died in there instead of constantly being pouting because that's all his character has to do right now), I don't think Calleigh Duquesne died during s5 'cause I actually enjoyed her during that season 'cause, hey she was so happy whenever I saw her interacting with Jake.
The problem with Calleigh began right after "Stand Your Ground", in my honest opinion. I still cannot belive she was brave enough
rolleyes
to accuse Jake of being the alcoholic one when she was the one who drank way too much, she was the one who created that mess...there were many other ways to escape from that inferno instead of shooting as if she had been in the farwest...but oh nooo Calleigh Duquesne was Miss Perfect and she couldn't face such thing, Jake was the one who drank too much and lead her to shoot her in the middle of the street.....that was insane in my opinion.
But, then again, I could try and understand her POV (though, I will never forgive her accusations against Jake....NEVER). What made me completely lose respect for her character, and I'm quite sure that the old Calleigh would have never done, was the whole cheat sheet stuff when she covered Eric. Ok she's a good person, she cares about the others...but my god she has a brain!!! Calleigh Duquesne would have used her brain!! Nope, this Calleigh had to remake her proficencies tests because she had to cover all Eric' shit 'cause that's what the guy had been making ever since his first bullet in the brain.
These things made me wish she would have died some time in the past. The fact most of us believe she "died" sometime between s5 and s5 lead us to speculate on a possible death during Going Under
Hope this post made sense