$1500 is exactly what they should do - but I am not afraid to ask for the $1800 model - I just im personally persuaded it would be foolish not to at least ask.
I guess it's just a difference in philosophy. It was a 2.2GHz "BlackBook" (not even Pro), so I'd be happy with pretty much anything in the MacBook Pro offered as a replacement. I certainly wouldn't expect an $1800 Mac in return. That said, there's no harm in asking (though I'd ask for the $1699 rMBP), but he should take $1500 if they don't budge (and I don't think they will).
To the OP, keep us posted. I'm sure you'll like whatever you get, as it will be a big improvement. I'm probably biased toward the Retina models since I was previously an Air user since February 2008 and am unfazed by the lack of legacy ports and drives.