Thanks all, and I agree this has been an interesting discussion, from what I thought to be cut and dry to a cloud if gray. I really appreciate all of your input.
@John Thedford Our agent has spoken to the FAR hotline, and the lawyer he spoke with said that we are right and the original contract is enforceable, they can refuse any concession/repairs but the original (FARBAR) contract stands despite rejection of the addendum.
@Franklin Romine No, they are actually serious about cancelling, and are refusing to go ahead even with absolutely no concessions based on inspection findings. Their agents broker is even involved, at this point, and sent a response to that effect. He actually sort of scoffed at the FAR hotline response vs his lawyers opinion.
@Rick Santasiere thanks for your input. I'll have to see if our lawyer can find a similar case if we decide to proceed. I think that our agent's logic in writing up an addendum rather than just continuing with the verbal was to make it clear that we weren't looking for them to do repairs plus $$ concession, just concession. Their agent appeared a bit confused to him so he wanted her to be clear when she spoke with her clients. I guess that this attempt to clarify has backfired on us big time!