Quoted from Bryan_Kelly:
Most here seem to be "glass half empty" kind of guys. Sure, there are lots of reasons not to do it. You could get hit by lightning tomorrow, too, but the odds are extremely slim.
I say go for it. It may be that personal touch that keeps your two companies in good graces.
I agree with Bryan. It would be different if they expected you to hand over your keys but since you will be there and be able to watch over things I say go for it! If anyone gets too drunk .... call a cab as you're responsible for them once they leave your place!