In the incident, on daf 50b, of the case that was brought to Rebbi concerning the chef who was hired to teach 1000 recipes and only taught 800, it is unclear what the final verdict of Rebbi was? Did the plaintiff win or lose the case? Any commentaries? Is this case discussed in any of the poskim?
I did not find any discussion of this particular case in the Poskim. If forced to Pasken this case I would accept the claim of the plaintiff. Although the deal was seemingly impossible to keep, still it does not go into the category of Asmachta. Asmachta can only free one of responsibilities accepted on an exaggerated condition. Hence, if the cook would have accepted a fine if he did not deliver, it could conceivably have been an Asmachta. We cannot, however, require someone to pay for services unrendered, no matter how ridiculous they are for those were the terms accepted (see Noda b'Yehudah, Choshen Mishpat I:30). The cook has the choice to deliver and get paid, or not to deliver. As for partial payment for what he did deliver, that conceivably would have to be retroactively re-negotiated and paid at the market rate.