Israeli film critic Yair Raveh links to this clip off the I Am Legend DVD, of the film's original ending.
To be honest, though it's obviously better than the tacked on upbeat ending the theatrical version shipped with, I don't think this ending works perfectly either. There would have had to be changes to the body of the film too, which stressed that the transformed humans were still feeling creatures. There are hints of this in the theatrical version, when the zombie male goes to extreme lengths to rescue the woman Smith's character captures for experimentation, but considering that we're talking about flesh-eating zombies who have all but depopulated the Earth, I think a little more effort, and a corresponding emphasis on the Smith character's monstrousness towards the zombies, were necessary to bring this point home. For all I know, though, that's on the DVD too.