I think this is great, and makes Padme's death more believable. I don't think she should have died immediately for several dramatic reasons within the film itself, not to mention the obvious Leia memory.

But to make sense of the rest of the film, Anakin's visions would have to be of her death by whatever other means, such as the idea of the disease or whatever. Though not my favorite story choice, Anakin's pursuit of dark power is motivated by his premonition that she would die.

I also wish there were some way to emphasize that Anakin did succeed in "keeping [someone] from dying." It'd be cool to show that his survival was entirely due to his use of the Dark Side, but even then he suffered a fate in many ways worse than death. This would emphasize the selfishness and futility of the Dark Side as well as its powerful capacity.