Legal Question in Construction Law in California

This is really a two-part question, because it presents an issue as to the liability of the estate for the decedent's debts AND an issue as to whether there is liability on an unsigned contract.

I'd say the estate is generally liable for the decedent's debts (I don't practice in the area of wills, trusts and estates, however). Now then, what is the estate's liability to the contractor, if any? Note that the law regarding home-improvement contracts requires that they be in writing and signed by the owner or his/her agent. So, the unsigned contract, if it falls under this law, is unenforceable. Even though oral contracts are often enforceable, this one wouldn't be.

However, the contractor isn't completely out in the cold, with no remedy. Courts are generally willing to allow the contractor to recover the fair value of the work performed and materials furnished under a "quasi-contract" (or "contract implied in law") theory, to avoid injustice. A quasi-contract isn't a contract; it's a legal fabrication created to allow justice to be done where it is clear that, although there is no contract, the parties intended their relationship to be contractual in nature. (Look it up on the Internet for further discussion).