I missed that, gingebee. Rather a silly thing for the cautious, careful Graham (spelling correction noted!) to say. With regard to Joe not being dead, I had the subtitles on and when Graham came back to the car minus Joe, it said something like "Sound of rustling water" - which I took to mean that the sound of the water was significant and the body had been dumped in the river.
I missed the bit where Cain hit Joe and didn't realise he was still alive when he was put in the car. So maybe he could come back at some point (although being dead didn't stop Dirty Den or Bobby Ewing from being resurrected).