We will answer your question with two reservations. First, we will limit ourselves to the letter of the law, not to considerations of compassion for a worker who got sick or to the intrinsic value of avoiding disputes. We leave these to you because they are voluntary elements and because there are too many subjective factors for us to relate to seriously without direct involvement. Second, we cannot rule conclusively on monetary matters without hearing both sides in the framework of a din Torah. We can only discuss your apparent rights and obligations based on your depiction. We hope this will give you a good point of reference.
It is now common for businesses to present package deals, as if you pay for one thing and get another free of charge. Sometimes, this is an accurate reflection of what the customer receives. For example, when one buys a car, he receives a key chain for free; the purchase is of the car alone and the key chain is a symbolic present. However, for example, if you agree with a contractor that he will provide twelve services in your home and he makes it worth your while by promising that four major ones will be free, the agreement is a package deal with one price for the total job. The four “free” services are included in the total price. While there are cases that fall into a “gray area,” it seems that you do not have to pay the full listed line-item prices for the work that was done. Rather, you may make a deduction from that amount because the work that was not done was “free” in name only (more specific details follow below). You are also correct that you are not required to accept future services as compensation for work that the contractor had promised but will be unable to carry out.
What happens when people arrive at a package deal of which only part is carried out as designed? Consider a precedent in the realm of sales. Reuven agreed to buy land and date trees from Shimon, but Shimon did not provide the trees. The Rambam’s ruling,[1] accepted by the Shulchan Aruch,[2] is that in such a case, the whole deal is off. The buyer can return the field and does not have to agree to compensation for the lack of trees. The Rama[3] accepts the opinion that the sale of the land stands, even though the full deal proved to be untenable, because we view the different elements as individual sales. In certain situations, however, all would agree that separate parts of a sale do not stand alone. For example, if someone tried to sell a large field but the sale could take effect only for some of it, the buyer can refuse to accept a purchase of the part of the field that is available, even at a reduced price.[4]
You, however, can certainly not void the entire deal at this point for a simple reason. Since you cannot “return” the services the contractor already provided, you must compensate him in some way for the work he did. Your situation is similar to the one described by the gemara,[5] which discusses a case in which Reuven rented a donkey from Shimon to transport wares and the donkey died along the way. Reuven has to pay Shimon for the part of the trip that the donkey carried out. The Rama[6] limits this to cases in which Reuven can salvage the situation by selling the wares in the place the donkey reached or by finding alternative transportation for the remainder of the journey. Otherwise, he need not pay because the incomplete job provided him no benefit. However, if there was benefit, even if the cost of finishing the journey brings the total cost to moderately more than the agreed price for the whole trip, Shimon still gets paid for the work the donkey did. We do not deduct the added cost when factors out of his control are responsible for the job being incomplete.[7] The same concept can be applied to work done by your contractor.
Therefore, in broad terms, the amount you halachically owe should be calculated as follows. Determine the relative market value of the work completed as a percentage of the whole job, including the bonus items. Multiply that percentage by the total price agreed upon (irrespective of whether it is the average price on the market). Use this amount as a basis for arriving at an appropriate agreement considering all the legal and human elements involved.