Hm. If you want a novel-length, angsty ride that doesn't get into identity until the second act, Beneath a Beating Sun has memory and identity as a major theme starting about halfway through – though Daniel is on the other side, trying to bring the alien intelligence around to see if it's really alien. (He does a lot of philosophizing. I think he's the main reason it ended up at 140-or-so k words instead of a much more sedate 60k.)

And then The Night, All Along is a short work on how Sam deals with the aftermath of a Legacy AU where she was infected with Machello's devices, and they didn't respect the Goa'uld markers and wound up driving her insane before Janet et al. could fix it.

I haven't done any more on the immediate aftermath of Full Circle/Fallen, though.