And what if you just resign and start a new game? After all you knew that game was won, so what do you lose? Just a few rating points (virtual rating points) which you will eventually recover in case you are that good.
The point is, I dont want to move on: It is them who have to resign instead of being that kind of scum.
Of course, if you block them, they will just sign up with a new account.
Block their IP? - Useless since most people are given a new IP each time they turn on their computer.
Best to just get over it and move on.
It has happened to me a few times (Like LongIslandMark, I've rarely had this happen). I just went and posted in their profile 'Leaving the game does not prevent you from losing, I can wait for my point. :)', then I find something constructive to pass the time like spreading my charm and wit in the forums.