I think it should work. If you die, you PC is stored in your local highscore list (with its own unique number). So if you restore backup save file and die again (or win), there would be two entries with same unique number in your local highscore list*. During synchronization, every character from your highscore is imported on server, not only those who managed to win the game. So if server imports my local highscore list (or just update) and detects two entries with same ID number, it would refuse to accept it - entries don't have to be flagged by "winners". Question is what if one entry made on your local high score, second did not. Well probably it can be worked around by storing PC unique numbers somewhere besides highscore, and numbers would be compared with every attempt to change highscore.
* This idea should actually work offline also.
@Blasphemous - all you wrote is true... but I still think save scumming is not a minor problem, as it is probably most common and easy (and at the same time effective) way to cheat. I don't think that many players uses cheat engine programs or even heard about them (for example I'm a long time Adom player and didn't heard about it up to this day).