A very interesting thread, and the idea has endless potential. There are so many things that can affect the outcome. I'd personally find it more intriguing if Dudley died in early childhood, it could lead to some very interesting changes. It would also be pretty IC of the Dursleys to disregard the nurse's warnings in the summer before GoF.

But what if this happened to Vernon instead? How would Petunia react? What would have happened if she'd committed suicide instead of taking Harry in?

So many creative ideas for the Dursleys' demise, so few of them used regularly.