Roxanne, you are awesome. I downloaded DLTC and after messing with things a few minutes I got it to work. I needed to do two things for this to work. First, I edited the script bd0108.bcs and I just removed Dynaheir's dead checks.
I then ran C:SetGlobal("Sprite_is_Deaddynaheir","Global",0) to undo the *ahem* unfortunate gnoll event so that I would be able to interact with her.
After this, when I got to the third floor, Minsc and Dynaheir spawned, as would have happened if I hadn't killed Dynaheir. It's also "my" Minsc, 19 STR, equipment, XP and everything, I didn't have to do anything special for this, so I assume it's EET keeping continuity. Dynaheir got a boost to 200k XP, while Minsc, who was already above this, didn't get anything.
I want to thank you for taking them time to help me with this, you made my day. Hamsters and Rangers everywhere rejoice!