This question begs for another question, what the fruit really was.
What does discerning of good and evil mean? Most people think discerning of moral good and evil, but there are different uses of this pair in the Bible. I believe it's ability to know/discern all opposites (such as gain and loss). In some Bible verses good and evil are used in this way, both separately and paired up. Notice that when Eve decided that the fruit was good and desireable to make one wise, she already thought in her mind that to eat was gain, and to not eat was loss - didn't she discern already and sin already by coveting in her mind?
I think this discerning was the fruit in and of itself, which made the eyes open. The ability to discern also automatically makes one subject to moral law because they become able to judge, and so they immediately saw they were naked. The fruit is our discerning ability, as the name implies.
Now, although Adam and Eve were real ancestors in Messianic bloodline this also illustrates mankind all at once, and I think the story is an allegory. That doesn't mean that Adam and Eve weren't real people themselves. The skins represent acquiring physical bodies. The snake represents DNA, aka being born human (as opposed to animal) and having intellectual abilities (cunning above all beasts). Another forum member mentioned to me earlier that the number of the snake's words in the Bible matches the number of chromosomes. The snake is condemned to not have legs (walk upright) and indeed the flesh will never walk upright. They are cast out "east of Eden" - east signifies beginning of a day, which means human lives have beginning and conversely an end ("thou shalt surely die") as opposed to God's existence and eternal life in Him without beginning and end. So this is about being born as human, lust of the eyes, sin and being subject to moral law and death, which are all things inseparable from the very human nature.
In short, I believe there was no way that things would have played out differently. By having intellectual ability mankind was sure to question God at some point to their own detriment, and God did it anyway, because He wanted some intelligent creatures in His garden (aka created world; Eden metaphor is used to refer to its primordial, uncorrupted state; 4 rivers are physical but are also a metaphor for "4 corners of the Earth" and waters of life flowing from God's domain...)