RE: How do I save this battery pack?
Shouldn't be a problem, IFF you're sure the other two cells are okay.
Rather than solder on the good cells, though, I would recommend that you solder a heavy jumper wire across the terminals where the removed cell used to be. LiPoly cells have aluminum tabs and aren't easy for mere mortals like us to solder. Manufacturers spot weld or use a special aluminum solder that isn't the most human-friendly substance.
It will still be 2000mAh (provided there isn't any other damage), but it will be a 7.4V 2-cell pack instead of an 11.1V 3-cell pack. Basically, you're lopping off 1/3 of the "displacement" (like replacing a .61 with a .40 glow engine). You won't have near the same power as before, so it may not be to your liking with your current power system.