Argh, somewhere I read a demolition of the idea of a yoyo weapon--I wish I could remember where it was! Oh well, one of these days....
Anyway, the central thesis of the demolition was that there's a big problem with a yoyo as a weapon. That problem is that it slows as it reaches the end of its string, which is precisely the opposite of what you want a good weapon to do (i.e. hit maximum velocity at the end).
The other thing is that if you bounce a yoyo off of someone, it's hard to recover, which negates the utility of having that well-balanced spinning thing on the end of a line.
It is quite possible to use a weighted rope or chain--witness the manriki-kusari, the suruchin, bolos, and all their relatives. You can also use faster recovery weapon such as a meteor hammer, which is basically a weight at the end of a 3-4 m line. But if you want to swat someone with a yoyo, I think generally you let it run out and swing it.
Oh well, I'm sure the next person on will have a sample of a filipino combat yoyo from the mountain tribes
, but that's my take
F