I'm thinking if Lucas had gone with "Episode I" in 75/76, you WOULD have seen "Darth Maul" or whatever he would have been named then, killing Anakin's father. If I remember, that was one of the story elements in the treatment and the rough draft--our hero, as a teenager, watches his father get cut down by a sith.

Gotta remember, if he'd gone with TPM, it wouldn't be the same as the TPM we got in 99. There'd be some differences, because he didn't already have 3 films worth of story to call back to. Details would have changed, like the above.