Thats a bummer about Baxter. As for the whole Slipper/Maafu thing, I would rather have the best player run on. If required, Slipper can shift to LHP to cover an injury to B.R. It is unlikely to have both he and Robinson receive an injury in the same game, and whether or not he starts on the bench, both he and Robinson would have to be injured for us to be without a LHP, so I believe the selection decision should come down to who is the more capable player. My vote (and I believe yours) is with Slipper.
From WAY out in the left field - has anyone thought about perhaps moving Giteau to outside centre for a game? Whilst I'm a massive fan of Horne, it'd be a great experiment to see what he can do with some more space. He really is an awesome ball runner and is brilliantly gifted in beating fractured defenses, so I can see him running wider. I think having him as a playmaker seems to be basically a ploy to get the ball in his hands more anyway, so why not put him in a position where his running skills can really come to the fore and play another running centre like Fainga'a inside him. I reckon it'd be magic if it worked (and shithouse if it didn't). Might be worth trying in a European tour match or something (maybe in a midweek game?).
AAC (Adam Ashley-Cooper) at inside centre could be an okay experiment too, though I love the way he plays fullback (and wing... and outside).