They did say that they might need to replace the shell (battery was slightly swollen in both machines) and that I'd be responsible for that cost, but that didn't happen for either box. I don't think they replace the shell unless it's really, really deformed. Neither of my machines would sit flat and both were obviously swollen. One I could practically spin like a top (and the trackpad was screwed).
I got both back with no deformities, a new battery, keyboard, and trackpad, and a 199 bill (plus tax).
I wouldn't rule out getting it fixed. If you do end up paying a little more, then you can probably sell it for more than the price it cost to fix.
Last time I looked I was quoted somewhere in the neighbourhood of $600 for a rMBP battery replacement - but that was just the battery. Even that IMO is not a reasonable cost for what it is - the only reason it costs that much is the fact that it's glued in, and the fact that Apple charge so much for the part.