In Nevada, a verbal contract, like any other contract, is enforceable if the elements of a contract can be proven. There are two principal differences between a verbal and written contract: (1) the verbal contract is harder to prove, and (2) the statute of limitations for enforcing verbal contract is 4 years, whereas you have six to bring claim on a written contract.
Nevada does not have a Dead Man's Statute. In fact, Nevada statute expressly provides, "Evidence is not inadmissible solely because it is evidence of transactions or conversations with or the actions of a deceased person."
Contact a contract attorney licensed in Nevada, and you'll get a better idea, based on the facts of your case, what your options are.