I always thought it would be more dramatic if Padme did not die, but was forced to chose which child to take to Alderran. Kenobi and Yoda could have told her because they are in danger being with the force, splitting them up makes sense that atleast one can survive if the other twin is found.

Then you could have a dramatic moment for Padme to chose which child to take. You could have her sobbing as she decides to take Leia, and Kenobi wisks Luke away to Tattoine. You could have her one more time arguing with Kenobi to keep both children, but in the end for their safety, she knows they are right. In a sense that would have been just as tragic as Padme dying, having her husband turn to the darkside and losing a child because they are in danger from him.

They could have then faked Padme's death at the end of ROTS, and assume she dies between III & IV, and then Leia remembering her mom would make sense, but still be dramatic.

The prequels.....what if......We could write a book on this stuff.