Hmmmm, nice point, Voice of Reason. I have been thinking on this since finishing the book, but had forgotten that Dumbledore said that two full wizards would probably not make it on the boat. So...if we are thinking of two people, one of them would need to be underage, a muggle or a squib. Hmmmm. I've been trying to be good all day at work, and now you've got me thinking again.

I like the idea of it being Regulus for the reasons that have been mentioned. I've also been thinking about Amelia Bones. But I have no reasons or proof, just wishful thinking maybe?