Look...if the decision was made to have Sophia killed in crossfire, then at the end of the movie was the exact right place for it to happen. For that moment to come any earlier in the film would've made the rest almost anti-climactic. Michael's heart would've been broken and his role of Don be diminished that much sooner. Wouldn't have worked (not that much in GFIII DOES work).

For first time and even repeat viewers, this ending DID have a pretty good impact. You're still reeling from the shock of Sophia's death and then fast forward about 20 years to Michael's own death...blind, crippled, alone. It's over.

Incidentally, with regard to the way people malign Mary's 'Dad....???' just before dropping to her knees and keeling over, I always thought that was pretty well done. It could be imagined that the bullet hit in such a way that she was literally stunned and didn't know what hit her.
I would guess FFC directed Sophia to play it exactly the way she did. One of the few memorable moments from a very non-memorable performance.

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