I think it's implied that both pairs are exactly the same as each other, but one gets to Vegas first and has more luck. 
Technically, the duplicate Stewie and the original Brian died, but that's a depressing thought!

Well the black guy said "somebody's getting torn open", and the only guy there was Brian, so quite possibly.

I laughed at the bit where Brian was telling Stewie about his 'escape' plan, by digging a hole in the garden, even though he has a car

Brian's Play was far better than Yug Ylimaf, or any other episode this season.

The deaths of unlucky Brian and lucky Stewie were quite dark in my opinion, but the short clip of them confronting each other in heaven was awesome, as was the segment with the surviving Brian and Stewie! It was a great episode, the "Country Club" one wasn't awful, but certainly not great.

Family Guy is only great nowadays when Brian and Stewie are the center piece for an episode. The fact that "Roads to Vegas" was mostly them was a breath of fresh air compared to some Family Guy crap.