Well if he detached OK, that's a big concern overall. Probably pretty small comparably, and he might have a harder time getting started (feeding, shedding, etc). Take care of him like you would do with the others. It would not be the first story I have seen with an unabsorbed yolk, and though I haven't dealt with it personally, I read ALOT about all things BP. I am sure a pro will comment in the morning to offer more encouragement
Did some research for ya. There are a few threads dealing with unabsorbed yolks, but they were still attached.