harry potter - What would Voldemort have done had he won?

This might sound like speculation, but can it be reliably predicted from canon what Voldemort would have done after he won, were he successful in defeating Harry and the Order?

Would he just rule over the wizard world and keep up the masquerade, or would he try to take over the whole Earth by starting a (dark-)wizard vs. muggle war?

Answer

He wouldn't have been content with simply ruling the Wizarding world. Voldemort hated his father for being a Muggle and no doubt resented being a half-blood wizard despite also being the Heir of Slytherin; he even went as far as to adopt a new name to disguise the fact he was related to a Muggle family.

I think the new statue in the Ministry of Magic when Voldemort has (secretly) assumed control gives a pretty clear indication of his thoughts about Muggles and what he would have done with them if he'd had free reign to do so:

Now a gigantic statue of black stone dominated the scene. It was rather frightening, this vast sculpture of a witch and a wizard sitting on ornately carved thrones, looking down at the Ministry workers toppling out of fireplaces below them. Engraved in foot-high letters at the base of the statue were the words MAGIC IS MIGHT.

...

Harry looked more closely and realised that what he had thought were decoratively carved thrones were actually mounds of carved humans: hundreds and hundreds of naked bodies, men, women and children, all with rather stupid, ugly faces, twisted and pressed together to support the weight of the handsomely robed wizards.
"Muggles," whispered Hermione, "In their rightful place. Come on, let's get going."

_{Deathly Hallows - Chapter 12, Magic is Might}